research methods in war studies and international relations

Conflict Analysis and International Relations

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• Karin Aggestam  

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Conflict analysis concerns the systematic study of the causes, actors, processes and resolution of conflicts around the globe. It draws upon a number of disciplines and strives to be conflict sensitive while generating relevant suggestions on how to manage and resolve conflict. The broad focus of conflict analysis is also reflected in the multitude of methodological approaches which are utilised (see, e.g., Druckman, 2005). This diversity partly relates to the differences in the overarching purpose of research. For instance, some studies strive to predict conflict behaviour and attitudes with the utilisation of game theory and/or simulation (Colaresi and Thompson, 2002; Maoz and Mor, 1996). Other studies aim for policy relevance and to bridge the theory-practice divide (Fisher, 2009). In such studies, structured focused comparison and/or single case studies methods are frequently used not only for theory advancement of conflict analysis, but also for generic and normative prescriptions. For instance, it may concern when and how specific conflict-resolution strategies are considered most efficient to be applied during a conflict cycle. Finally, a growing number of studies use ethnography and narrative as methods to unravel the complexities between identity politics, specific contextual features of conflict and global structures (Auerbach, 2009; Jutila et al., 2008; Nesbitt-Larking and Kinnvall, 2012). In short, the fields of research and practice of conflict analysis are vast (Monroe et al., 2009).

• Foreign Policy
• International Relation
• Belief System
• Restorative Justice
• Political Elite

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Aggestam, K. (2014). Conflict Analysis and International Relations. In: Nesbitt-Larking, P., Kinnvall, C., Capelos, T., Dekker, H. (eds) The Palgrave Handbook of Global Political Psychology. Palgrave Studies in Political Psychology Series. Palgrave Macmillan, London. https://doi.org/10.1007/978-1-137-29118-9_9

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The debates of methodology and methods: reflections on the development of the study of international relations

Review of Economics and Political Science

ISSN : 2631-3561

Article publication date: 12 May 2021

This paper aims to explore the interplay between methods and methodologies in the field of international relations (IR) over the 100 years of its lifetime reflecting on the relationship between the rise of new research methods and the rise of new methodologies.

Design/methodology/approach

This paper looks in retrospect into the field’s great debates using a historiography approach. It maps chronologically the interplay of methods and methodology throughout the stages of the development of the study of IR.

This paper argues that inspite of narratives of triumph being common in the field, the coexistence of competing research methods and methodologies is the defining feature of the field. All theories, all methods and all methodologies have undergone a process of criticism, self-criticism and change. New methodologies have not necessarily accompanied the rise of new research methods in the field.

Originality/value

Drawing a map of the field’s methodologies and methods reveals necessarily its dynamism and its plurality. An honest map of the field is one that highlights not only theoretical differences but also ontological, epistemological and methodological differences embedded in the field’s debates.

• Research methods
• Methodology
• Historiography
• Post-positivism

Abou Samra, A. (2021), "The debates of methodology and methods: reflections on the development of the study of international relations", Review of Economics and Political Science , Vol. ahead-of-print No. ahead-of-print. https://doi.org/10.1108/REPS-06-2020-0063

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Copyright © 2021, Amira Abou Samra.

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Introduction

International relations (IR) theorists, especially since the second half of the 20th century, had been inclined to consider concerns over ontology, epistemology and methodology to fall outside the scope of their interest, to be of concern to the field of philosophy ( Hay, 2006 ). Today, however, as IR theory is witnessing its “fourth debate,” quite frequently described as a “metatheoretical debate,” these concerns are no longer dismissible. There is a growing awareness that discussions over methodology have been marginalized in favour of discussions over theories and that this is something that needs to be remedied ( Chernoff, 2007 , p. 2).

This paper argues that learning about the theoretical assumptions, without paying due attention to methodological and methodical aspects behind them, leaves researchers halfway through, either blinded to the plethora of possible alternative ways available to deal with political reality or rather totally unequipped to deal with it. Whilst highlighting the methodological and methodical debates that have been going on in the field, this paper argues that telling the history of the relationship between research methods and methodology is an important alternative way of telling the story of the field debates, leading to the appreciation of deeper differences and similarities between its paradigms and theories and to the answering of important questions about methodological plurality in the field, the meaning of science and future concerns for the study of IR.

Hence, the paper is not concerned with the great debates of the field as such, but rather interested in drawing a historiographical map of field debates in a way that specifically addresses the interplay between methodology and methods, seeking, thereby, to answer a number of questions: If it is common to highlight changes in the research methods of the field by referring to two basic tracks, the traditionalist-behaviouralist-post-behaviouralist track and the positivist, post-positivist track ( Mostafa, 2016 , pp. 57–70; Mosafa, 2010 , pp. 840–846), where do methodologies diverge and converge in these two tracks? What is the relationship between the emergence of new research methods and the emergence of new methodologies in IR? How does literature in the late 1980s exploring a methodological turn in IR ( Little, 1991 , pp. 463–478) differ from literature in 2017 lamenting over an overdue methodological turn ( Kanfo, 2017 )? Do new research methods and new methodologies coexist with old ones? Do they necessarily compete? If methodology is the process of establishing scientific inquiry ( Kaplan, 1964 , pp. 22–24), what impact does the existence of multiple methodologies have on the meaning of science?

For conceptual clarity, methodology and research methods fit into a matrix of interconnected and interrelated concepts as broad as epistemology, ontology, methodology and theory. In philosophical traditions, “ontology” corresponds to the study of being or existence, where the answers to major questions about the relationship between human beings, the universe and nature are reflected upon. The ontology generates a specific view of knowledge, that is, the epistemology. Epistemology answers questions such as: What can we know and what are the sources of knowledge? What is the purpose of knowledge? Is “certain” knowledge ever achievable? Is the development of knowledge and science progressive in nature so that newer theories necessarily carry more knowledge than older ones? The epistemology provides the background foundation for all theorization. Directly derivable from the epistemology are both the ontology of the field and its methodology ( Abul-Fadl, 1994 ; Krauss, 2005 ).

It is important to distinguish between the philosophical understanding of ontology, where ontology as a theory of existence serves as a driver of epistemology, a theory of knowledge and methodology as a process of producing science on the one hand, and between ontology in the understanding of the field of IR, where the word “ontology,” though borrowed from philosophy, stands for the content of political reality in the field, e.g. “identities, individuals, social collectivities, states, regimes, systems, or some combination of the above.” ( Hay, 2006 ). Ontology in social sciences answers also the question of “what is reality,” hence, whether reality has a solid and an independent existence from researchers or whether reality is just “fluid and constructed the result of human perception and claims about it” ( Lacatus et al. , 2015 ).

Methodology is defined by Abraham Kaplan (1964 , pp. 22–24) as “the logic of scientific research”; the process by which science is produced. Kaplan’s definition of methodology is broader, even more neutral, than definitions that, later on, directly link methodology to empiricism, whereby empiricism is a methodology used to “form theoretical claims and to test their empirical implications.” In such a narrow definition of methodology only what is empirically testable, hypotheses that can lend themselves to falsification by being subjected to a test of reality, is science ( Sprinz and Wolinsky-Nahmias, 2004 , p. 4). This definition of methodology is inseparable from a definition of theory that regards theory as a set of assumptions to be tested against reality for accuracy, validity and quality ( Sprinz and Wolinsky-Nahmias, 2004 , p. 4).

In its broad definition, however, methodology refers to a process that produces science. Even if that science is not testable against reality; for so many reasons, amongst which might be the belief that there is no neutral or independent existence of reality that it can be tested against to begin with, as will be furtherly explained throughout the paper.

Ultimately, what one considers as “science” and what one accepts as “theory” are products of what one believes in, epistemologically, ontologically and, by consequence, methodologically.

Methodology produces theories that end up producing or making use of approaches or research methods which answer the question: What are the specific steps that the researcher must follow to get to answer his research question?

This paper is divided into two main parts looking in retrospect into the debates of the field, chronologically mapping the interplay of methods and methodology through the stages of the development of the study of IR. The first part, divided into three sections, tells the story of the development of the study of IR over a time span of around 60 years until the end of the 1970s or mid-1980s which mark the beginning of the “relative” demise of the behaviouralist “hegemony” over the field.

The second part of the paper, divided into three sections, covers the period starting from the relative “demise of the empiricist positivist promise for a cumulative positivist science” in the late-1970s and mid-1980s until our present time ( Little, 1991 , p. 463), asking whether the past four decades have brought along some methodological turn in IR or simply a shift in research methods and techniques.

Part I: traditionalism-behaviouralism-post-behaviouralism

Traditionalism vs. behaviouralism: from the science of advice to the science of grand theories.

The positivist enlightenment project though produced in Europe, flourished and boomed in the USA. Positivism was and still is a dominant feature of the American understanding of social reality ( Smith, 2000 , p. 375). Behaviouralism as a positivist methodological approach to the study of political science had its origins in the USA in the 1920s and 1930s and has been usually associated with the University of Chicago and the works of Charles Merriam ( Grigsby, 2011 , p. 15). Behaviouralism was influenced by behaviourism ( Hafner-Burton et al. , 2017 , pp. S1–S3), a school of psychology reflecting positivism, a “belief in the infinite possibilities of science” and “in the powers of the human mind,” where logic and reason constitute the only source of all certain knowledge ( Herakovic, 1983 , p. 10). In behaviourism, human behaviour can be simplified to the extent that it can be measured in the here and now without any reference to past experiences or inner motives ( Herakovic, 1983 , pp. 70–82). Human behaviour can be observed, monitored and interpreted based on its external features ( Hamati-Ataya, 2012 , pp. 3–4). Behaviourist assumptions were influenced by the “stimulus and response idiom”, and were, hence, advocating that living organisms – be they animals or human beings – interact with all forms of external stimuli in a manner that seems to be quite uniform. Behaviouralism was furtherly influenced by the behaviourist belief that “the same laws that governed the physical world could be applied to human nature,” hence came the appreciation for controlled laboratory experiments and empiricism, where the senses are the main sources of knowledge. Although behaviouralism later on distinguished itself from behaviourism ( Hamati-Ataya, 2012 , pp. 3–4), behaviourism’s impact on social sciences in general and political science in particular could not be mistaken. Behaviourism had already been influential in other social sciences since the past decades of the 19th century ( Davis, 1965 ; Smith, 1989 ). There, “tough minded empiricism overthrew the hegemony of the moral philosophy of the seventeenth and eighteenth centuries” and carried along an “epistemic transformation” to social sciences ( Davis, 1965 ; Smith, 1989 ) replacing “absolute sources of truth” with the “boundless belief in the powers of the human mind” ( Herakovic, 1983 , p. 10). This is why the behaviouralist turn in IR was not just a methodological turn, but rather mainly an epistemic turn.

In the field of IR, behaviouralists in the 1950s were propagating to be the missionaries of a “scientific revolution,” endorsing the following set of basic assumptions:

First, IR as an independent social science: Behaviouralism advocates the ability of IR to exist as an independent social science. That advocation stands in deep contrast to a traditional perception of IR as a common/joint research area shared by many fields and sciences – such as philosophy, law, economics and even political science ( Finnegan, 1972 , p. 40). Interestingly, behaviouralism borrowed approaches from other fields such as mathematics, physics, biology, economics, sociology and psychology, hence not only from natural sciences but also form social sciences that were already witnessing a behaviourist turn, fields that traditionalism did not consider as relevant to political science though ( Hamati-Ataya, 2012 , p. 5).

Second, the unity of scientific knowledge: behaviouralists considered IR (as a social science) to be quite similar to the natural sciences, where description, measurement, observation and quantitative, mathematical and statistical tools were essential research tools. Traditionalists rather considered IR to be closer to humanities, closer to literature and philosophy, where analysis and contemplation were key to understanding international reality.

Third, science is value-free: In contrast to the traditional perception in which values are inseparable from science and where, therefore, history, political theory and law are indispensable to the understanding of the international phenomenon ( Chernoff, 2007 , p. 2); behaviouralism promoted the possibility of establishing an objective, value-free science in which researchers play a completely neutral role. The reproducibility of knowledge is a key behaviouralist assumption; just by following the same steps, researchers anywhere can get almost the same results ( El-Hayagna, 2001 , p. 111).

Fourth, the possibility of producing major and general theories in IR: A good theory in traditionalism is to be tested against history, political theory and law ( Chernoff, 2007 , p. 2). Behaviouralism claims a good theory is a simple theory that depicts as “less complex causal mechanisms” as possible. Hence, it relies on measurable variables for explaining, even predicting phenomena under study ( El-Hayagna, 2001 , pp. 83–89).

The behaviouralist-traditionalist divide is much more than a divide over research methods; it is a divide over the appropriate methodology for producing “science,” with some clear epistemological and ontological aspects of divergence that will be furtherly discussed in the following section.

Rise of behaviouralism: a journey not void of criticism

Traditional approaches to thinking about political reality were quite prevalent in political science in the early 20th century ( Druckman et al. , 2006 , p. 627).

The early beginnings of the field in the aftermath of the First World War seemed strongly influenced by the ideas of idealists. The likes of the idealist Wilson were driven by a desire to “guide the conduct of states in their IR (towards a more peaceful world), rather than focusing on the actual behaviour of states” ( Hellman, 2011 , p. 18). This explains why the study of IR from an idealist perspective was guided by an interest in political philosophy, international law and diplomacy, the approaches quite familiar to traditionalism ( Hellman, 2011 , p. 18).

Behaviourialism in the field of IR had many critics along the process of its relative rise – Hedley Bull and Stanley Hoffman just to name a few ( Hamati-Ataya, 2012 , p. 17).

Some criticized the fact that behaviouralist studies overlooked cultural diversity and ignored the richness of human experience ( Dyer and Mangasarian, 1989 , p. XVII).

Some criticized behaviouralist claims about the existence of value-neutral science, especially given the growing tendency to equate “observation” with “quantification.” Although behaviourialism did not completely displace values from scientific research, it limited its study to the empirical manifestations of values. An interest for values in a normative sense was relegated to the realm of political philosophy ( Hamati-Ataya, 2012 , pp. 7–10).

Growingly, some warned against the dangers of being “attached to spurious statistical and mathematical correlations” drawing, therewith, the attention to the importance of “testing sophisticated statistical methods” for “real correlations, questioning the significance of these correlations in the absence of human judgement to evaluate them” ( Forward, 1971 , pp. 18–20).

Strikingly, some behaviouralists seemed to struggle with their own behaviouralism. They complained about the lack of data and the confidentiality of many aspects of relations between states. They struggled with the large number of variables affecting IR and with the absence of a clear classification for them. They even complained about cultural and social differences they encountered whilst studying states, a discovery that seemed to impede their pursuit of general laws ( Davis, 1965 , pp. 15–16).

Obviously behaviouralism was not walking its way of empirical political analysis in the absence of research difficulties or amidst general satisfaction. Behaviourialists – in a way maybe comparable to post-positivists today – complained even about their inability to communicate easily with decision-making circles and to influence them ( Forward, 1971 , p. 20).

But the criticisms of behaviouralism – from Europe mainly and sometimes from within the USA itself – did not prevent the spread of behaviouralism, even in Europe ( Hamati-Ataya, 2012 , pp. 6–7).

Although behaviouralism – as previously mentioned – was mainly a product of an American social and political context ( Hamati-Ataya, 2012 , p. 2) and was originally loaded with epistemological, ontological and methodological claims driven from the particularity of positivist enlightenment ( Herakovic, 1983 , p. 10), the traditional-behaviouralist debate – most probably under the influence of the behaviouralist disinterest in philosophy – was usually presented as a debate over appropriate research methods, rather than a debate over the appropriate scientific methodology or the philosophy of science itself. The debate ignored the questions of what constitutes science and whether social sciences have a distinct nature from natural sciences, questions that remained vibrant in the field of philosophy at that time ( Little, 1991 , p. 468).

Looking in retrospect, however, it makes a lot of sense to talk about behaviouralist methodology, not only behaviouralist methods, although the advocation that behaviouralism is charged with epistemological, ontological and methodological content was not that common during the rounds of traditional-behaviouralist debate.

According to Richard Little (1991) , the methodological difference between traditionalists and behaviouralists – though existing since the very beginning – remained unexplored in the field of IR at least until Kenneth Waltz introduced his neo-realist theory in the 1970s ( Little, 1991 , p. 446). The following section explains this statement. The section revolves around the relationship between behaviouralism and realism on the one hand and behaviouralism and neo-realism on the other hand and how the emergence of neo-realism influenced the methodological and methodic debate taking place in the field of IR.

Behaviouralism and realism: the joint journey

With the end of the Second World War, the field became more receptive to realist assumptions. To realism, some attribute the credit for shifting the study of IR from the “science of international values and ethics” – that many have lost their faith in as a result of the Second World War experience – to the “science of studying power and interest” ( Badran, 2000 , pp. 71–72). This obviously was not only implying an ontological shift, moving away from the study of what ought to be to the study of what really is. It was implying an epistemological shift from transcendental meanings of right and wrong, good and bad to a man-centred definition of interests and morality. Many of the realists advocated the need for a general explanatory theory of IR ( Forward, 1971 ; Davis, 1965 ; Hamati-Ataya, 2012 ). Behaviouralism, therefore, was highly compatible with the realist needs, the former allowed for “the pursuance of Realism’s scientific aspirations with the emerging methods and techniques of the age” ( Hamati-Ataya, 2012 , p. 12). The realist-behaviouralist partnership set the stage for their mutual rise within the field.

Maybe the relative rise of behaviouralism can be explained by the field’s longing for a more predictable international environment that is subjectable to accounts of reason and logic to encounter a dangerous Cold War international environment ( Forward, 1971 , p. 20) or just a by-product of the American victory in the Second World War; just a triumph of the knowledge preferences of the more powerful; saying nothing about the quality or worth of behaviouralism per se . Anyway, many consider the period after the Second World War to be the period of the “second and serious foundation of the discipline” dedicated to the reconstruction of a US-led world order ( Ekkehart Krippendorff, 1987 , p. 57). So, and regardless of possible explanations for that, the behaviouralist empirical studies presented themselves from the 1950s onward as the only possessors of a “scientific methodology” in IR ( Chernoff, 2007 , pp. 79–130). Studies sometimes even still refer to behaviouralism as the “scientific approach” to the study of IR, a label that might misleadingly suggest to the unexperienced reader that only behaviouralism is capable of producing “scientific” knowledge in the field.

Under the behaviouralist-realist collaboration, many research methods/approaches were introduced to the study of IR, amongst the most famous of which are rational choice methods such as the game theory, the decision-making approach in foreign policy, etc., mainly oriented towards the study of great power politics with special emphasis on questions of war and military conflict ( Forward, 1971 ).

Of particular importance is the shift in the thinking about the study of IR brought along by Kenneth Waltz (1979) . Waltz, arguably a behaviouralist himself ( Dolan, 2014 , p. 59), directed serious criticism to behaviouralists.

Waltz’ theory revolved around the assumption that anarchy restricts the behaviour of states, forcing them to adopt a conflictual-competitive attitude in a way that reproduces this anarchy over and over and guarantees the continuity of the state system itself. Waltz claimed that the global failure to develop a general IR theory is explicable by the failure of IR theorists to understand this methodological background from which all theories and approaches should depart. To Waltz, his neo-realist systems theory was not just a theory, it was the only viable methodology in IR.

Already as early as the 1970s and 1980s, Waltz’s theory came under scrutiny, especially with the emergence of neo-liberalism and neo-Marxism. The neoliberal theory criticized Waltz’s insistence on ignoring non-competitive forms of relations between states such as those embodied in developments of international law and international institutions ( Little, 1991 , pp. 463–466). On its part, neo-versions of Marxism mainly criticized the claims of systems theory that political power was distributed almost equally between states, because these claims remained oblivious to power relations between different social groups ( Linklater, 1986 , pp. 301–312). These criticisms set the stage for what will become known as the neo-realist, neo-liberal, neo-Marxist debate and later on as the inter-paradigm debate ( Hoffman, 1989 , pp. 60–61), embracing theoretical plurality in the field ( Little, 1991 , p. 463). Interestingly, some of the most prominent neoliberal and neo-Marxist theories were behaviouralist theories, the neoliberal institutionalism and the neo-Marxist Wallerstein’s world-system theory are but examples.

More importantly, in opposition to Waltz’s claim of being in possession of the only scientific methodology, some studies in the field of IR began to raise doubts – finally explicitly – about what the philosophy underlying knowledge in the field of IR should be, whether the field had ever actually been comparable to natural sciences with static laws built in the structure of the universe itself, whether IR was not rather similar to humanities ( Ferguson and Mansbach, 1988 , pp. 656–657). These criticisms were directly targeting the positivist understanding of the world underlying the behaviouralist project and its theoretical advocates – be they neo-realist, neo-liberal or neo-Marxist, reopening, therewith, the way for history, political thought, culture and values to influence the study of IR ( Badran, 2000 , pp. 69–96).

It is important to note that the failure to explain and predict the end of the Cold War was not the only shortcoming of Waltz’s theory. Reality kept surprising neo-realists, whose theory could not later on explain things as major as the continued existence of NATO, inspite of the end of the Cold War ( McCalla, 1996 , pp. 445–475) or developments in the integration process of the European Union.

Theoretical promises to provide exhaustive answers were not fulfilled even in the case of a theory as popular as Waltz’s, declaring, thereby, that realism cannot become a “methodology” for studying IR as Waltz wanted for it to be, but more importantly declaring the “demise of the empiricist positivist promise for a cumulative behavioural(ist) science” ( Little, 1991 , p. 463).

The accumulated criticism to the behaviouralist scientific project would acquire sometimes the title of “post-behaviouralist revolution” ( Hoffman, 1989 , p. 60), revolting against some essential behaviouralist assumptions:

Some post-behaviouralist studies criticized the marginalization of history, the history of the West and the history of peoples around the world in a way that impoverished “the content, the perspectives and tools of IR theory” ( Ekkehart Krippendorff, 1987 , p. 28).

Moreover, some studies criticized the marginalization of normative theorizing in IR, the deliberate neglection of nonmaterial aspects of international politics. For example, the English school would direct serious criticism to the absence of “normative inquiry into the relationship between order and justice,” and social constructivism would complain about the negligence of the role of norms in shaping states’ identities and interests ( Reus-Smit , 2009a, 2009b , p. 66).

Worth noting also is how some studies criticised behaviouralist claims of science being value free and produced early attempts at highlighting some relationship between knowledge and interests by criticizing an American hegemony over the field. Some noted that behaviouralist IR theorizing managed to make the behaviour of the USA become a standard and everyone became dedicated to “justify the unique and frightening accumulation of power in conjunction with the world mission of the United States of America,” rather than challenge or even criticize it ( Ekkehart Krippendorff, 1987 , p. 28).

Post-behaviouralist criticisms to behaviouralism seemed to reiterate many of the traditionalist concerns about the utility and quality of behaviouralist theorizing in IR. However, advocating these criticisms were now several separate theories that began to emerge throughout the late 1970s, 1980s and 1990s: the English school, the postmodern theory, the social constructivist theory, the feminist theory, etc. These theories would gradually line up in the face of the three theories of the inter-paradigm debate. The latter would collectively be called the traditional theories or the mainstream theories of IR ( Sprinz and Wolinsky-Nahmias, 2004 , p. 5). This would leave the field in an unprecedented state of – basically ontological and methodic – fluidity far from being able to agree on the core aspects of the international study such as the main actors, the main issues or even the nature of international processes as vital as globalization itself, growingly realizing that the mainstream theories in the field were incapable of catching up with the complexity of reality and its rapidly changing nature ( Mostafa, 2016 , pp. 70–98).

Criticisms would evolve to produce two different calls in terms of methods and methodology. The first call will defend and retain the positivist character of the field, opening up only to a plurality of research methods, whereas the second call will defend the need for a completely new research attitude towards IR, advocating a post-positivist methodological turn in IR. In the following part, these two calls and the ensuing developments will be tackled in some detail.

Part II: from post-behaviouralism to post-positivism

Easy way out: a call for reconciliation between research methods.

Early responses to criticism to behaviouralist approaches came in the form of calls for “reconciliation” between quantitative – using tools such as statistical analysis, regression coefficients, simple mathematical calculations – and qualitative approaches to international political analysis – using tools such as event analysis, case study, content analysis, interviews, comparisons, etc. ( Mahoney and Goertz, 2006 , pp. 227–228) ( Boassen, 1991 , pp. 192–207), acknowledging some of the analytical shortcomings of quantification and accepting a degree of plurality of research methods in the field. Here, shortcomings of behaviouralism were addressed by responses at the level of research methods, rather than the level of methodology.

Obviously, quantitative and qualitative studies were still supposed to “worship the same (positivist) God,” where science is all about testable observation, even if they disagreed on smaller goals, qualitative studies producing “cause of effect explanations” and quantitative studies producing “effect of cause explanations” ( Mahoney and Goertz, 2006 , pp. 227–228).

A similar conclusion was reached by Sprinz and Wolinsky-Nahmias who believed “methodological pluralism” became a necessity ( Sprinz and Wolinsky-Nahmias, 2004 , pp. 7–8). It is important to note that their reference to methodology is closer in meaning to “approaches or research methods,” rather than methodology as a process of scientific inquiry. This is because the advocated plurality of quantitative and qualitative approaches remained a plurality within the confines of an understanding of science as testable observation, embodying the logic of causation. Enough proof is that a one-third of studies published in prominent journals were discarded from the analysis of Sprinz and Wolinsky-Nahmia’s study – though calling for methodological plurality – because of being “devoid of scientific methodology,” i.e. because of being descriptive and historical ( Mahoney and Goertz, 2006 , p. 8).

Hence, the emergence of qualitative studies as such did not undermine the positivist epistemology and its related methodology in a way that would justify a real methodological distinction between qualitative and quantitative research. It is important not to confuse the positivist qualitative approaches with the post-positivist qualitative approaches to be discussed later on.

Still in the 21st century, admitting the deficiencies of behaviouralism is not an easy task for its advocates. Rather than criticizing the product of empirical behaviouralism, some explained the failure of behaviouralist studies to provide sober political analysis for major events by the failure of behaviouralist studies to grasp the real essence of experimentation, claiming that behaviouralist studies never really conducted an experimental study “in the sense of controlled manipulation as when a single factor is modified, whilst holding everything else constant,” what they did was rather closer to non-experimental empirical tests far from satisfying the “modern meaning of experimentation” ( Druckman et al. , 2006 , pp. 628–629). Here, behaviouralist studies failed, because they were not behaviouralist enough.

Yet, although the advocates of behaviouralism are obviously still far away from being disenchanted with it, most of them have become disenchanted with the goal of reaching a general theory in IR. Instead, the goals of experimental research – whatever the definition of experimentation – have become much more modest serving three purposes: searching for facts to “adjucate disputes” in cases in which studies seem to reach contradictory results, to test the accuracy of certain theoretical assumptions and to advise the political leadership ( Druckman et al. , 2006 , pp. 632–633).

So, new was just a degree of humility about the ability to generalize the conclusions of quantitative studies and a degree of humility about the limited ability of quantitative and experimental research to address some specific research areas, such as the study of civil wars, terrorism or regime stability ( Druckman et al. , 2006 , p. 633), all leading to the above highlighted calls for a reconciliation between qualitative and quantitative approaches.

Anyway, according to this view, the traditional descriptive research methods remain inferior to the quantitative or qualitative research methods that allow the production of studies based on “testable observation.” Traditional approaches pay attention to philosophy, history, values and law in a way that neither these quantitative nor qualitative approaches recognize as “scientific.”

It is not surprising that this very same path will lead today to the so-called “revival of behaviouralism” ( Hamati-Ataya, 2012 , p. 19) or the “new behavioural revolution” ( Hafner-Burton et al. , 2017 , pp. S1–S3) in which contemporary behaviouralism is becoming more modest about the formulation of general theories, is becoming more aware of psychological influences on rationalization, is providing alternatives to or complementing rational choice models and is shifting its goal to the explanation of “the causes and consequences of heterogeneity across actors, including (deviation) from rationalist expectations” ( Hafner-Burton et al. , 2017 ; Mintz, 2007 ) rather than searching for similarities. This explains the interest of contemporary behaviouralists in neuroscience and neurobiology in the study of foreign policy and diplomacy, for example ( Hamati-Ataya, 2012 , p. 19). Obviously, these studies have not abandoned the dream of establishing a science very similar to the natural sciences nor did they give up on the value of an empirical understanding of reality.

Calls for a return to experimental research are on the rise because of technological and software advances that highly improve the results of this kind of research, even allowing for the emergence of new experimental approaches such as the multi-investigator experimental survey or the use of laboratory experiments to explore the impact of media, for example ( Druckman et al. , 2006 , p. 630).

Some even advocate the “end of theories,” meaning the decline in the need for explanatory models. They claim that the role of human beings in interpretation and analysis could be dispensed with. That role is now performed by the machine, which – relying on a huge amount of information; the big data – can make sound enough decisions on its own ( Moawad, 2020 , pp. 9–14). It is interesting to note how these calls maintain the same early behaviouralist tones of the value free science – only in a more modern language – where the role of researcher in the research process itself is reducible to that of a neutral observer, now even replaceable by an advanced computer.

Regardless of different assessments of the contemporary weight of behaviouralism, there is no doubt that behaviourialism has left a highly influential impact on the field of IR in its contemporary form. Even amongst the most informed academic circles, it still does not go without resistance to introduce studies in IR that are not based on testable observation. Cherishing the behaviouralist contribution to IR, Inanna ( Hamati-Ataya, 2012 , p. 20) wonders what the field would have looked like, if it had not been for behaviouralist insistence not to surrender:

[…] to the easier options of either asserting transcendental truths with no concern for their empirical accuracy or impact on human life, or of offering a loosely descriptive account of the world from an uncommon-sense, or introspective perspective.

Exactly because of this continued appreciation of a positivist understanding of the social world, the road ahead of post-positivist theories in the field of IR has not been that easy. The following section addresses some of the challenges facing post-positivist methodology and research methods in the field.

Overdue confession: positivism is not the only viable scientific methodology

The reconciliation between qualitative and quantitative research methods and the reconsideration of the possibility of formulating general theories in IR have only addressed some aspects of criticism directed at behaviouralism. In the corridors of the theory of IR, other aspects of criticism directed at behaviouralism were still lingering. Some theoretical developments would cast serious doubts about the positivist understanding of neutrality and objectivity, about the quality of the political analysis that ignores nonmaterial aspects such as ideas, values, interpretations and about the nature of political reality and its independent existence from researchers trying to understand it. It is these critical trends that would gradually draw attention to a metatheoretical relationship between neo-realism, neo-liberalism and Marxism, the theoretical trilogy that Rennger [quoted in ( Hamchi, 2011 , p. 214)] described as variations of “the same traditional Western epistemology and its methodological correlates – rationalism, positivism and pragmatism,” even though the three of them were supposed to be rivals.

By the late 1980s, calls would emerge to acknowledge an implicitly ongoing process of “(meta)theoretical restructuring of international relations theory” ( Neufeld, 1995 , p. 3), calls drawing attention to the emerging critical post-positivist theorizing.

“Post-positivism” is a quite ambiguous label. The term has been used at different stages of the development of the study of IR to describe different kinds of theoretical contributions. In the 1970s and 1980s, those dissatisfied with the behaviouralist obsession with a value-free science focusing mainly on the material aspects of the social world were sometimes referred to as post-positivists. This explains why the label “post-positivism” was granted to early contributions from the English school, social constructivism, feminism, etc. ( Reus-Smit , 2009a, 2009b , p. 66). Later, the label “post-positivism” will be more cautiously granted only to change seeking/reflexive/deconstructive, rather than problem-solving ( Eun, 2017 , pp. 593–607), contributions in the field, as a result of some growing awareness that a mere concern with values or other non-materialist aspects of the social phenomena is not a guarantee of a different mode of scientific theorizing – not a guarantee of a departure away from positivism ( Hamchi, 2011 ; Wiener, 2004 ).

Actually, it makes a lot of sense to claim that many of the theories that would fall today under the critical post-positivist category have a positivist version as well. This explains one classification of theories in the field that distinguishes between positivist critical theories and post-positivist critical theories ( Lamp, 2020 ). Feminism is different from critical feminism, and conventional or classical constructivism is different from interpretive/critical constructivism, even the critical theory itself has at least two generations ( Neufeld, 1993 ; Neufeld, 1995 ).

This is partly the reason why IR literature disagrees on how to label this mainstream-critical divide, whether to call it a third debate or a fourth debate ( Diez and Steans, 2005 , p. 127) to clearly distinguish it from a third debate that accepted theoretical plurality and opened up gradually not only to neo-liberal and neo-Marxist contributions but also to a feminist theory, a green theory, a constructivist theory, etc., a plurality that would, nonetheless, still be placeable under the umbrella of positivism.

Post-positivism departs from a complete set of alternative assumptions

First, theoretical reflexivity: theories are not just neutral descriptions of interactions between social actors (states, individuals, organizations, etc.). Whilst positivist theories develop hypotheses to be tested against reality ( Neufeld, 1990 , p. iii), post-positivist theories consider the “givens” of reality as non-given; as products of the theory itself, therefore, reality can never really become the judge of good theory ( Diez and Steans, 2005 , pp. 129–130).

Besides, how a researcher chooses his topics, how he selects his research methods and how he interprets or understands them is a derivative from his research preferences ( Ferguson and Mansbach, 2020 ), from his intellectual and political interests and from the historical setting that shapes his understanding of reality, i.e. his “historical circle” ( Diez and Steans, 2005 , p. 139). Bias is embedded in all theories regardless of how objective or neutral they claim to be. This is why realism is usually identified in this literature as an ideology that served the goals of establishing an international system with American hegemony after the end of the Second World War ( Ferguson and Mansbach, 2020 ). Knowledge can, therefore, only be understood within a context of time, space and interests ( Krauss, 2005 , p. 759).

Post-positivist theorizing warns against “self-fulfilling and self-defeating prophecies” that result from “people theorizing about the behaviour of people” ( Diez and Steans, 2005 , p. 141). Theories play a role in shaping the world which in turn is continuously reproduced in a way that reflects the understandings of the theories that seek to understand it. Leaders believing in realism will only see an international environment fraught with perils, they will most likely act according to a realist logic, even though they know of the existence of international cooperation or others, leading thereby to the fulfilling of realist prophecies about a world of anarchy and self-help ( Krauss, 2005 , p. 759).

Second, interpretivism: the post-positivist reflexive methodology conflicts with the logic of causation. It distinguishes between constitutive and causal relationships, taking pride in producing knowledge beyond what is observable, tangible, measurable and empirically testable ( Diez and Steans, 2005 , p. 141). No matter how similar behaviours appear to be, the difference in the real motives and the “uninterpreted facts” behind them necessarily makes them widely different from each other ( Ferguson and Mansbach, 2020 ). Therefore, quantitative and mathematical research tools for analysing international reality are far from sufficient, just in a way similar to the understanding of a language, where knowing the rules of grammar and the meaning of words is not enough for understanding what people say; the motives behind the words would make a true difference in meaning ( Diez and Steans, 2005 , p. 138).

Third, commitment to social change: post-positivist theorizing has a fundamental function of social criticism oriented toward emancipation, giving preference to change over stability and over the maintenance of the status quo by solving its problems ( Chernoff, 2007 , p. 131), believing in the creative role of human consciousness to guide the process of change ( Neufeld, 1990 , p. 3). The ability to subject one’s own assumptions to self-criticism is just an innate feature of post-positivist theorizing; continuously re-evaluating their commitment to change and emancipation, reassessing the extent to which their theorizing has managed to rid itself of Eurocentric, modern and positivist biases, thereby quite often producing new versions of the same theory at every stage. Though self-criticism is usually a point of strength, it sometimes seems to impede the ability of critical post-positivist theorizing to provide some stable, accumulated theoretical structures (Abou Samra, 2016, pp. 1409–1508).

Fourth, a commitment to plurality: post-positivist theorizing will draw the attention to the irony embedded in the dedication in non-Western peripheral academic circles to a consumption of the American positivist scientific project, inspite of its shortcomings in grasping the essence of non-Western reality or representing non-Western interests ( Jones, 2004 ).

Though post-positivist literature seriously acknowledges cultural diversity and its impact on the understanding of IR, it is important to note that the fourth debate remains a debate confined to theories competing within a secular world view. Even if the human mind is unable to explain all the aspect of political reality with reference to what is observable and empirically testable as post-positivists believe, the hidden part of the phenomenon remains produced – according to them – by social interactions ( Ekkehart Krippendorff, 1987 , pp. 29–30). “The emancipatory reference for critical theory is immanent to practices of the society itself, rather than an external, transcendental criterion for ethical judgement” ( Oliveira, 2018 , p. 9). Some reflection on alternative non-secular answers to questions of IR follows in the conclusion.

Post-positivism evaluated

The evaluation of the contribution of post-positivist theories to the field is quite controversial. Critics hold them responsible for turning the field into a field of “isolated theoretical islands” with no particular subject, characterized by fluidity in the absence of a clear-cut methodology ( Lamont, 2015 , p. 13), turning the field into a field where anything goes ( Ferguson and Mansbach, 2020 ). Critics accuse post-positivist theories of being unable to answer the most important questions in the field on how to explain war or how to maintain peace between states ( Neufeld, 1995 , pp. 330–331), even of being normative and detached from reality.

It is important to note that most of these criticisms depart basically from an inability to acknowledge the post-positivist methodology as a viable “scientific” methodology ( Ferguson and Mansbach, 2020 ). Obviously, many of the theorists – who accepted relatively easily some plurality of research methods, failed to welcome a plurality of methodology, even less a plurality of epistemologies ( Smith, 2000 , p. 375).

Post-positivism, in these criticisms, seems to be judged against the dictates of a methodology that it came to revolt against. Post-positivism is not there to better provide causal explanations of reality, it is there to better change reality.

In return, many cherish the fact that the post-positivist stage of the development of the study of IR has brought some serious novelty into the field at the level of approaches and research methods.

First, inspite of their diversity, post-positivist theories will appear to complement each other, rather than compete against each other ( Diez and Steans, 2005 ). This is not to be confused with the neo-neo consensus, acknowledged since the 1990s, for example ( Jackson and Sorenson, 2003 , p. 128), where neo-liberals and neo-realists, though having much in common, will remain competing against each other. Post-positivist theories are mutually reinforcing, their approaches are reciprocated and their concerns and aspirations for changing international reality are shared. That is why compound titles such as critical feminism, feminist post-colonialism, critical constructivism and deconstructive linguistic approaches are quite familiar ( Achilleos-Sarl, 2018 , pp. 34–46). Concepts such as emancipation, deconstruction and the power of knowledge are well known in post-positivist literature in a way that seems better representative of real plurality, where all theories are capable of complementing each other, whilst maintaining their unique characteristics and assumptions.

Second, post-positivist theories have developed, sometimes borrowed, some unique multi-levelled research approaches.

At one level, the assumptions of post-positivist theories themselves will serve as approaches to IR. It is quite common to encounter the terms feminist approach, post-colonial approach or poststructuralist approach ( Hesse-Biber and Leavy, 2006 , p. 105). Here, the mere elaboration of the post-positivist critical assumptions and the mere exposure of biases, both in theory and in reality, against the excluded, the weak and the marginalized in different social contexts become a research goal in itself ( Tickner, 2020 , p. 628).

At a second level, some specialized research methods were developed sharing the goal of making “the voices of the voiceless heard.” Here, critical post-positivist theories quite often rely on interdisciplinary approaches – approaches from the fields of philosophy, linguistics, literature, history, sociology and anthropology. These approaches are also quite often referred to as “qualitative research methods,” but they differ greatly from the positivist qualitative methods previously addressed. All post-positivist qualitative approaches share the assumption that reality is not independent of those who seek to understand it, and they work on revealing biases behind common sense understandings of reality. The ethnographic approach, focusing on everyday life and global processes, dealing with experiences as diverse as life in refugee camps and online shopping ( Windsor, 1989 , pp. 229–270), and the discourse analytic approach, focusing on the construction of realities through political discourse ( Jackson, 2007 , pp. 394–426) are some telling examples of such approaches.

At a third level, “metatheoretical approaches” emerged in the field, addressing the level of the metatheory of IR; the epistemological approach, with the Afrocentric feminist epistemological approach being an example ( Hesse-Biber and Leavy, 2006 , pp. 80–84), the constructive engagement approach, revealing cultural similarities at the level of philosophy ( Dottin, 2019 , pp. 40–41), are but examples of approaches revealing biases against non-mainstream epistemologies and contemplating on power relations existing at the levels of epistemology, ontology and methodology.

Post-positivism is, therefore, credited with a gradual expansion of the field of IR, theoretical and methodological expansion, disciplinary expansion – beyond IR and political science, substantive expansion and territorial expansion beyond the West ( Hellman, 2011 , p. 21).

An overview of the development of the study of the field reveals a complex interplay between theories, methodologies, research methods and reality. It is quite difficult to say whether the neo-realist relative failure – in the face of the end of the Cold War – caused the demise of the empiricist behaviouralist project or whether the failure of behaviouralism to grasp the aspects of the international phenomena left the neo-realist theory – and later on the neoliberal and neomarxist theories – with limited analytical resources in the face of a highly complex world in which poverty, climate change, religious resurgence, even epidemics seem to be not less dangerous to human existence than wars, free trade and the spread of capitalism – the issues of utmost priority to traditional IR theories. By the same logic it is quite difficult to say, whether the emergence of post-positivist research tools was the result of new developments in reality that were not understandable using positivist techniques, or whether the post-positivist tools have made us identify some aspects of reality to which we were completely insensible. For sure, post-positivist theorizing managed to expose some biases built into our understanding of IR; biases favouring the white, the male, the Western, the secular, the rich, the materially powerful, the rational, etc. ( Grosfoguel, 2007 , pp. 211–223). The interplay between reality on the one hand and theories, methods and methodologies in IR on the other hand is undeniable and quite complex.

Besides, although the narratives of the field prefer to tell the story of the triumph of realism over idealism, the triumph of behaviouralism over traditionalism and the triumph of American positivism over non-positivist alternatives, an overview of the methodological history of the field, in its first 60 years, showed that neither realism, nor behaviouralism, nor positivism have ever gone uncriticized in the field, not even in the 1960s or 1970s which used to be considered as the heydays of these scientific endeavours. In the past 40 years, these very same endeavours have been continuedly challenged in a way that further raised doubts about stories of “triumph,” at least stories of absolute triumph.

One conclusion, therefore, is that the field has never really surrendered to advocates of “the single scientific methodology” discourse. Throughout its development, calls for embracing theoretical plurality, methodic plurality, methodological plurality, epistemological plurality, etc., have been a recurring feature of IR.

It makes sense to claim that the field of IR has witnessed not only methodic plurality but also methodological plurality through the stages of its development. Different research methods and different methodologies – though sometimes highly critical of each other – seem to coexist in the field of IR to this day. Years of fierce theoretical debates just led to the de facto coexistence of behaviouralist, empirical, statistical, mathematical, qualitative and quantitative research methods on the one hand and post-positivist, reflexivist, deconstructivist and interpretivist research methods on the other, reflecting methodic plurality and methodological plurality. Nothing is sacred in IR; all theories, all methods and all methodologies have undergone a process of criticism, self-criticism and change. Drawing a map of the field’s methodologies and methods reveals necessarily its dynamism and its plurality.

The impact of the whole paradigmatic understanding of IR on methodologies and methods is sometimes subjected to serious criticism, because it restricts knowledge, making one unaware of a lot of things just because they fall outside the scope of concern of their adopted paradigm, hence, making researchers “method driven rather than problem driven” ( Hellman, 2011 ).

The need to sometimes cross the strict boundaries of theoretical frameworks has been acknowledged under different labels; analytic eclecticism proposed by Sil and Katzenstein is one of them, where a degree of interdisciplinarity and a degree of complementarity between different approaches of different theoretical traditions become highly cherished ( Sil and Katzenstein, 2010 , p. 417).

However, the rise of new theories and the rise of new research methods have not necessarily been accompanied by the rise of new methodologies. Positivism – in its methodological aspects – has been underlying much of the theories of IR, even those that present themselves as rivals such as neorealism, neoliberalism, some main strands of the English school or of constructivism.

More importantly, positivism – in its aspects as a secular theory to existence – remains the dominant underlying view of positivist and post-positivist theorizing in IR.

This paper has basically reflected on the interplay between methodology and methods as manifest in the Western course of development of IR theory. An emerging non-Western research course has been deliberately left out for future research. An “Islamic Civilizational Paradigm of IR” would clearly distinguish itself from positivism and post-positivism, calling, thereby, upon a methodology that combines reason and revelation and research methods that comfortably accept this duality ( Mostafa, 2016 ; Abou Samra, 2019 ). Attempts at developing a Chinese theory of IR – though strongly benefitting from a constructivist turn – would suggest the importance of making use of Chinese philosophical heritage ( Noesselt, 2012 ). A Chinese theory and an Islamic paradigm are just but examples of many emerging non-Western alternative theoretical understandings of IR reflecting cultural particularity. These reflections even furtherly suggest that a plurality of methodologies and methods can go far beyond the positivist and post-positivist understandings of a world making one wonder how different IR in the age of a truly “global IR” can look like ( Acharya and Buzan, 2017 , p. 7), a stage opening up slowly and somewhat hesitantly to diverse understandings of reality, history, life and existence from around the world.

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Further readings

Akinyoade , D. ( 2012 ), “ Ontology and epistemology for peace and conflict studies ”, International Conference on the Security Sector and Conflict Management in Nigeria (University of Ibadan, Nigeria), 14-16 August .

George , S. ( 1976 ), “ The reconciliation of the ‘classical’ and ‘scientific’ approaches to international relations ”, Millennium Journal of Scientific Studies , available at: https://journals.sagepub.com/doi/pdf/10.1177/03058298760050010301

Lapid , Y. ( 1989 ), “ The third debate: on the prospects of international theory in a post-positivist era ”, International Studies Quarterly , Vol. 33 No. 3 .

Lapid , Y. ( 2020 ), “ 25 years after the third debate: two (pianissimo) bravos for IR theory, the ‘third debate’ 25 years later symposium ”, available at: www.isanet.org/Publications/ISQ/Posts/ID/304/25-Years-after-The-Third-Debate-Two-pianissimo-bravos-for-IR-Theory ( accessed 2019 ).

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In This Article Expand or collapse the "in this article" section Process Tracing Methods

Introduction, debates about case studies and case-based methods.

• Productive Account / Systems Approach to Studying Mechanisms
• Minimalist Approach to Studying Mechanisms
• Bayesian Approaches
• Non-Bayesian Approaches
• Case Selection and Combining Process Tracing with Other Methods
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Process Tracing Methods by Derek Beach LAST REVIEWED: 26 March 2020 LAST MODIFIED: 22 April 2020 DOI: 10.1093/obo/9780199743292-0227

Process tracing is an in-depth within-case study method used in the social sciences for tracing causal mechanisms and how they play out within an actual case. Process tracing can be used to build and test theories of processes that link causes and outcomes in a bounded population of causally similar cases, in combination with comparative methods, or, when used in a more pragmatic fashion, to gain a greater understanding of the causal dynamics that produced the outcome of a particular historical case. The strength of process tracing is that detailed knowledge is gained through the collection of within-case, mechanistic evidence about how causal processes work in real-world cases. Process tracing enables only within-case inferences to be made, making comparative methods necessary to enable inferences to causally similar cases. Comparisons make generalization possible because we can then claim that as a set of other cases are causally similar to the studied one, we should expect similar mechanisms to also be operative in these cases. Process tracing as a method can be broken down into three core components: theorization about causal mechanisms linking causes and outcomes, the development and analysis of the observable empirical manifestations of the operation of parts of theorized mechanisms, and the complementary use of comparative methods to enable generalizations of findings from single case studies to other causally similar cases.

To understand what process tracing is as a distinct case study method, it is important to have a good working knowledge of the underlying realist philosophical foundations of case-based methods. A wonderful and comprehensive introduction to different philosophical foundations of different social science methods can be found in Jackson 2016 . Good introductions to realist philosophy can be found in Maxwell 2012 and Sayer 2000 . It is also important to understand the core methodological debates about what case studies actually are. After the publication of Designing Social Inquiry ( King, et al. 1994 ), considerable debate has arisen about whether small-n methods, including case studies and small-n comparisons, constitute a distinct research approach or whether they can be subsumed under an overarching logic of studying variance. The “case-based” approach is articulated in Brady and Collier 2011 , George and Bennett 2005 , Goertz and Mahoney 2012 , Ragin 1987 , and Ragin 2000 , among others. This approach argues that small-n comparisons and within-case study methods, like process tracing, build on ontological and/or epistemological foundations different from “variance-based” approaches. The “variance-based” approach to case studies—including process tracing—is described in King, et al. 1994 and in Gerring 2017 . Here single cases are disaggregated into multiple “cases” in order to assess the difference that variance in values of a cause (or intervening variables) have for values on the outcome across units of the case.

Beach, Derek, and Rasmus Brun Pedersen. Causal Case Study Methods: Foundations and Guidelines for Comparing, Matching and Tracing . Ann Arbor: University of Michigan Press, 2019.

The book explores the foundational differences between case-based and variance-based approaches and develops a set of guidelines for using case-based comparative methods and process tracing.

Brady, Henry E., and David Collier, eds. Rethinking Social Inquiry: Diverse Tools, Shared Standards . 2d ed. Lanham, MD: Rowman & Littlefield, 2011.

Influential edited volume that explores different aspects of case-based research, including differences with variance-based approaches, and discussions of what types of evidence within-case analyses can use.

George, Alexander L., and Andrew Bennett. Case Studies and Theory Development in the Social Sciences . Cambridge, MA: MIT Press, 2005.

Influential book that developed core ideas about process tracing as a distinct research method, along with structured, focused comparisons and congruence case studies.

Gerring, John. Case Study Research . 2d ed. Cambridge, UK: Cambridge University Press, 2017.

Introduction to case study methods from a variance-based perspective.

Goertz, Gary, and James Mahoney. A Tale of Two Cultures: Qualitative and Quantitative Research in the Social Sciences . Princeton, NJ: Princeton University Press, 2012.

A very useful introduction to the core elements of case-based methods taken as a whole. Less helpful regarding how to use process tracing in practice.

Jackson, Patrick Thaddeus. The Conduct of Inquiry in International Relations: Philosophy of Science and Its Implications for the Study of World Politics . 2d ed. London: Routledge, 2016.

DOI: 10.4324/9781315731360

Influential book that explores the foundational philosophical assumptions underlying social science methodologies, including neopositivism, (critical) realism, pragmaticism and analyticism, and reflexive approaches.

Johnson, R. Burke, Federica Russo, and Judith Schoonenboom. “Causation in Mixed Methods Research: The Meeting of Philosophy, Science, and Practice.” Journal of Mixed Methods Research 13.2 (2019): 143–162.

Useful overview article that discusses different understandings of causation, including a mechanistic account that is distinguished from counterfactual and regularity accounts.

King, Gary, Robert O. Keohane, and Sidney Verba. Designing Social Inquiry: Scientific Inference in Qualitative Research . Princeton, NJ: Princeton University Press, 1994.

DOI: 10.1515/9781400821211

Classic but controversial book that argues that cases should be disaggregated into multiple “cases” in order to investigate the difference that variance in the values of independent and intervening variables makes for the outcome.

Maxwell, Joseph A. A Realist Approach for Qualitative Research . Thousand Oaks, CA: SAGE, 2012.

Great introduction to realist philosophy that develops an interpretivist epistemological stance while at the same time arguing for process understandings of causation as well as causal complexity.

Ragin, Charles C. The Comparative Method: Moving beyond Qualitative and Quantitative Strategies . Berkeley: University of California Press, 1987.

Classic book that develops some of the foundations for case-based methods.

Ragin, Charles C. Fuzzy-Set Social Science . Chicago: University of Chicago Press, 2000.

Book that introduces more advanced comparative techniques (qualitative comparative analysis [QCA]) within case-based methods. QCA is a useful tool in combination with within-case studies using process tracing.

Sayer, Andrew. Realism and Social Science . London: SAGE, 2000.

DOI: 10.4135/9781446218730

Concise introduction to critical realism that develops the distinctions between the real-actual-empirical, and that discusses the nature of causal mechanisms.

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Modern Deterrence Theory: Research Trends, Policy Debates, and Methodological Controversies

Department of Political Science, University of Missouri

Department of Political Science, University at Buffalo, SUNY

• Published: 02 May 2016
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Modern deterrence theories were conceived in the aftermath of World War I. Given the human and political carnage associated with the Great War, it was natural for historians, military strategists, policy analysts, diplomats, and politicians to try to understand why the breakdown occurred. The standard interpretation of the coming of World War I provided the intellectual foundation for classical deterrence theory and its variants. This article traces these developments in the literature of war and conflict initiation and evaluates recent theoretical, empirical, and policy challenges to mainstream realist theory. It summarizes two synergistic variants of the classical specification of deterrence and contrasts them with competing explanatory frameworks, then examines the empirical literature on deterrence, recent theoretical developments in deterrence theory, and debates about deterrence policies. It concludes with a discussion of how the study of deterrence fits into the study of international conflict more broadly.

Although modern deterrence theories (there are more than one, and there are several variants) are generally traced back to the start of the Cold War period, they were actually conceived in the aftermath of World War I, a conflict that was brought about by the most massive failure of deterrence in the history of the international system ( Maurer 1995 ). 1 Given the human and political carnage associated with the Great War, as it was known at that time, it was quite natural for historians, military strategists, policy analysts, diplomats, and even politicians to try to understand why the breakdown occurred. Over time the accumulated understanding of its genesis provided the intellectual foundation for contemporary realist theories of the causes of war and, most important for our purposes, for classical deterrence theory. There is a straight theoretical line from Carr (1939) through Morgenthau (1948) to Brodie (1946 , 1959 ), Schelling (1960 , 1966 ), and Waltz (1979) that takes as its starting point “a specific interpretation of a single historical episode: the coming of the First World War during the July Crisis of 1914” ( Trachtenberg 1990/1991 , 76).

Our purpose in this article is not only to trace these developments in the literature of war and conflict initiation, but also to evaluate recent theoretical, empirical, and policy challenges to standard realist theory. We begin by summarizing two synergistic variants of the classical specification of deterrence theory and contrast them with competing explanatory frameworks, particularly perfect deterrence theory. After that we examine the empirical literature on deterrence, recent theoretical developments in deterrence theory, and debates about deterrence policies. We conclude with a discussion of how the study of deterrence fits into the study of international conflict more broadly.

Theories of Deterrence

If modern deterrence theories were born in the wake of World War I, they came of age as World War II was winding down. By that time, the contentious debate between liberal and realist thinkers was seemingly resolved ( Carr 1939 ). In short order, realist thinkers came to dominate strategic discourse in both academic and policy-making circles, and “power” emerged as the defining concept of the period (e.g., Morgenthau 1948 ). If Brodie (1946 , 76) was right that, after Hiroshima and Nagasaki, the chief purpose of military forces was not to win wars but to avert them, then skillful power management would be required. Almost to a theorist, realist thinkers saw a balance of power as the structural condition necessary for peace to prevail—that is, for deterrence to work. Indeed, at the dawn of the Cold War era, balance of power theory constituted the conventional wisdom of the field. Thus, it is more than understandable that the first wave of modern deterrence theorists ( Jervis 1979 ) took as axiomatic the pacifying nature of a strategic balance. According to former Soviet spymaster Pavel Sudoplatov (1994 , 195), some of the West’s leading scientists believed so strongly in the positive relationship between peace and a balance of (atomic) power that they passed sensitive information derived from the Manhattan Project to the Soviets: “Since [J. Robert] Oppenheimer, [Niels] Bohr and [Enrico] Fermi were fierce opponents of violence, they would seek to prevent a nuclear war, creating a balance of power, through sharing the secrets of atomic energy.” 2

Balance of power theory, however, was constructed on a weak empirical base ( Vasquez 1997 , 903). For instance, it is now well understood that World War I was waged under parity conditions, leading Kenneth Waltz (1993 , 77) to observe that “if … an ‘equality of power … among the major powers’ minimizes the likelihood of war, World War I should never have been fought.” Predictably, some modern deterrence theories were adjusted to take cognizance of this fact and a new variable, the cost of war, was called on to explain away the empirical anomaly. In consequence, two distinct, albeit synergistic, strands of realist theory were developed, each of which rested on what Gaddis (1986) called the “twin pillars” of deadly nuclear weapons and a carefully managed strategic balance: structural deterrence theory and decision-theoretic deterrence theory .

Structural deterrence theory focuses on the interplay between system structure and the cost of conflict to explain the absence of war during the Cold War period. By contrast, decision-theoretic deterrence theory explores the same question within a choice-theoretic framework. Together, these two strands of realist theory constitute what we refer to as classical deterrence theory, which is the dominant paradigmatic articulation of deterrence theory. 3

Structural deterrence theory is associated with two major propositions about the dynamics of deterrence:

Under parity conditions, the probability of war is monotonically related to the cost of warfare, or as Mearsheimer (1990 , 19) has put it, “the more horrible the prospects of war, the less likely it is to occur.” Thus, when the cost of war is, or is believed to be, low, war is possible. But as the costs of war increase, it becomes, ceteris paribus , less and less likely. And since in the nuclear age the cost of war is exorbitant, rational wars are all but impossible. Accidental wars, however, can always occur regardless of their cost.

By contrast, asymmetric distributions of power are associated with crises and war. When military capability, nuclear or otherwise, is unevenly distributed, deterrence is unlikely to succeed. Under these conditions either the weaker state will give in to blackmail (or as George [1993] would call it, “coercive diplomacy”) or the more powerful state will simply attack and enforce compliance to its demands. 4

Given these propositions, a number of policy recommendations follow. For example, most structural deterrence theorists oppose a policy of minimum deterrence; rather they argue for an overkill capability that raises the cost of war and, in their opinion, reduces its probability. For a similar reason they oppose both significant arms reduction agreements and comprehensive and effective missile defense systems. Logically consistent structural deterrence theorists also support the “selective” proliferation of nuclear weapons. 5 For example, some time ago Mearsheimer (1990 , 54) argued that a German nuclear capability was “the best hope for avoiding war in post-cold war Europe.” And more recently, Kenneth Waltz (2012) made the case that a nuclear Iran would enhance rather than detract from the stability of the Middle East.

Consideration of the cost of war seemingly enabled structural deterrence theorists to explain away empirical anomalies such as World Wars I and II, both of which occurred under parity conditions. Unfortunately, other discrepancies between theory and fact remain. To wit, unless they make ad hoc adjustments to their underlying theoretical construct, structural deterrence theorists are unable to explain why, early in the nuclear age, the United States did not attack the Soviet Union when it enjoyed, first, a monopoly on atomic weapons and, shortly thereafter, a clear-cut strategic advantage; why the Soviet Union did not exploit its preponderance over China when these two states were at loggerheads in the late 1960s and the early 1970s; or why, more generally, states have failed to jump through so-called windows of opportunity whenever they have existed ( Lebow 1984 ).

Given these empirical shortcomings, it should not be surprising that several competing structural theories of great power conflict have been developed. Of these, power transition theory ( Organski 1958 ) is the most well-developed. 6 And although Elman and Jensen (2014) categorize power transition theory as a realist theory, its underlying assumptions are starkly different than those of the dominant paradigm.

In the realist paradigm the international system resembles Hobbes’s state of nature; it is a self-help system without an overarching authority to enforce agreements. But where realist theorists see anarchy, power transition theorists see order. To be sure, the order is imposed—by a dominant power that is largely satisfied with the system it controls and benefits from. Such a system is seen as stable unless and until a dissatisfied challenger capable of contesting the status quo emerges. Clearly, for this condition to be satisfied, the challenger must have a reasonable chance of extracting concessions from the dominant state in an all-out conflict; that is, its power must approximate that of the dominant state. Parity, however, is seen as a necessary but not as a sufficient condition for great power wars (i.e., for deterrence failures). Peaceful power transitions are always possible. Nonetheless, ceteris paribus , war becomes more likely as the speed at which a rising challenger’s power base approaches that of the dominant state increases.

On its face, power transition theory is consistent with the fact that all major power wars since Napoleon’s time have been waged under parity conditions; it also explains the absence of war during the earliest stage of the Cold War ( Organski and Kugler 1980 ). Power transition theory, therefore, rests on a much firmer empirical foundation than structural deterrence theory. Nonetheless, as a theory of the necessary but not sufficient conditions of major power war, it leaves open a key question about the onset of war in the international system: Under what conditions will peaceful power transitions take place (i.e., when will deterrence succeed), and under what conditions will a peaceful transition fail to materialize (i.e., when will deterrence break down)? 7

It is clear that structural theories in isolation are unable to fully answer such fine grain questions; that is, that they are by nature largely indeterminate ( Keohane 1986 , 182–183). For specificity, a theoretical structure that takes account of human agency is required. Not surprisingly, classical deterrence theorists have also developed a strand of theory pitched at the individual level of analysis. Previously we have referred to this part of the deterrence landscape as decision-theoretic deterrence theory. And although this part of the literature includes work on deterrence that employs both expected utility theory and certain psychological choice frameworks, game-theoretic models have been dominant.

Decision-theoretic deterrence theory can be seen as a synergistic analogue to structural deterrence theory. Structural theorists conclude that in the nuclear age, in which the cost of war is exorbitant, rational wars are all but precluded. Decision-theoretic deterrence theory assumes the same. Unfortunately, as we show next, the seductive assumption that war is irrational leads to a logical inconsistency.

Consider Figure 1 , which is a simple extensive-form game model of a one-sided deterrence relationship. There are two players in this game, Challenger and Defender. Challenger, who by assumption makes the first move, has two choices: to cooperate or to defect from cooperation. Cooperation ends the game and results in the outcome called Status Quo ; defection brings about a subsequent choice by Defender. Should Challenger defect, Defender will have two choices (responses): to concede to Challenger’s demands, in which case the outcome is Challenger Wins , or to defy Challenger, in which case the outcome is Conflict (or war).

Rudimentary Asymmetric Deterrence Game (Defender’s Threat Is Not Credible)

The assumption that the cost of war is exorbitant is reflected in the players’ preference assignments, which are given as an ordered pair beneath each outcome in Figure 1 . The first entry in each pair denotes Challenger’s relative rank of that outcome; the second entry, Defender’s. The outcomes are ranked from best to worst, with each player’s most-preferred outcome assigned a “3,” its second most-preferred outcome a “2,” and its least-preferred outcome a “1.” Notice that the outcome called Conflict is the lowest-ranked outcome (i.e., 1) of both players.

The assumption that conflict is the worst outcome for both players is the defining assumption of decision-theoretic decision theory and is entirely consistent with the supposition that the cost of war in the nuclear age is prohibitive. Nonetheless, at the same time, it is inconsistent with the proposition that bilateral nuclear deterrence relationships are inordinately stable.

To see this, consider first Defender’s rational choice at node 2, which will only come about if and when Challenger defects at node 1. Since Challenger Wins is assumed to be Defender’s second most-preferred alternative, and Conflict is its least preferred, Defender—if it is rational—will choose to concede whenever it is faced with a choice at decision node 2. But if a rational Defender will concede at node 2, then a rational Challenger should defect at node 1. Should Challenger cooperate at node 1, its second most-preferred outcome, the Status Quo , results. By contrast, defection will bring about its most-preferred outcome, Challenger Wins . All of which is to say that the assumption that Conflict is a mutually worst outcome is inconsistent with the assumption that deterrence will succeed as long as the players are rational. Yet classical deterrence theorists, of either the structural or decision-theoretic persuasion, continue to contend that bilateral relationships between nuclear equals are inherently stable.

To resolve this, the paradox of deterrence, decision-theoretic deterrence theorists have offered a number of solutions, the most ingenious of which can be traced to the creative mind of Thomas Schelling (1960 , 1966 ). Perhaps Schelling’s most well-known, if not his most notorious, resolution of the paradox rests on Defender’s ability to convince Challenger that it is not rational, that it will execute a suicidal threat to retaliate despite the costs and despite its interests. If Defender is successful, then a rational Challenger will cooperate at node 1, since defection will only lead to its worst possible outcome.

But this tactic, which is sometimes referred to as the “rationality of irrationality,” fails to resolve the paradox; nor does it help to explain why the United States and the Soviet Union did not attack one another during the Cold War period. To understand why, assume for a moment that the United States is able to deter an attack by convincing the Soviet Union that it will—irrationally—retaliate. If this is the case, how then can one explain why the United States did not attack the Soviet Union? To say that US decision makers failed to upset the status quo to avoid the cost of nuclear war is simply another way of asserting that they were rational. Clearly any argument that simultaneously assumes that a player is rational when it is deterred, and irrational when it is deterring, lacks logical consistency.

Another suggestion, not only of Schelling but of numerous other decision-theoretic deterrence theorists as well, is for Defender to make an “irrevocable commitment” to retaliate. Such a commitment could be made in a number of ways. For example, in the run-up to World War I a British official asked Ferdinand Foch, the French general and military theorist, “What would you say was the smallest British military force that would be of any practical assistance to you in the event of a contest such as the one we are considering?” Foch replied, without hesitation, “One single private soldier, and we would take good care that he was killed” (quoted in MacMillan 2013 , 402). Foch was implying that the death of even one British soldier would force Britain to intervene on France’s behalf should Germany attack.

Schelling argued that US forces stationed in Europe during the Cold War served a similar function, that is, as a “tripwire” that committed the United States to defend its NATO allies. But as intuitively appealing as this argument is, as long as the assumption is that Conflict is a mutually worst outcome, it still requires an irrational choice by a player and therefore fails to satisfactorily resolve the paradox of deterrence.

Much the same can be said of Schelling’s (1960 , ch. 8) “threat-that-leaves-something-to-chance.” Underlying this tactic is the supposition that while it may be irrational for a player to execute a deterrent threat, it may be rational to threaten to unleash an “autonomous risk of war” outside of a player’s control. A challenger might be deterred, then, if the risk of an accidental or inadvertent war is unacceptable, that is, is high enough.

Unlike other suggestions to resolve the paradox of deterrence, Schelling’s “threat-that-leaves-something-to-chance” stands on firm logical ground. Powell (1987) proved this some time ago. Unfortunately, it is not the logical foundation of this potential resolution that fails to suffice; it is its empirical basis. To wit, there are no known examples of accidental conflicts ( Maxwell 1968 ), and that includes World War I. The idea that the belligerents simply “slithered” into World War I, to use David Lloyd George’s famous phrase, that it was an unintended conflict, has largely been discredited ( Lieber 2007 ; Trachtenberg 1990/1991 ; Zagare 2011 ). If there is anything that seems uncontested in the most recent scholarship on the Great War, it is the fact that it was brought about by human decisions ( MacMillan 2013 , 537). 8

Another way to think about the obvious disconnect between assumption and conclusion is in terms of the credibility of each player’s threat. In the strategic literature, credible threats are generally taken to be threats that are believable ( Smoke 1987 , 93). But threats can be believed only when they are rational to carry out ( Betts 1987 , 12); thus, only rational threats are considered to be credible ( Lebow 1981 , 15).

If a credible threat is a threat that is rational to carry out, then the assumption that Conflict is a mutually worst outcome is tantamount to an assumption that all deterrent threats lack credibility. The reason is straightforward. As demonstrated in the discussion of the game in Figure 1 , given the assumption that Defender prefers Challenger Wins to Conflict , its rational response at node 2 is to concede. And since it is irrational to execute the threat, it must perforce be unbelievable or incredible.

That deterrence should fail when a defender’s threat lacks credibility should be no surprise. What is surprising is that many who understand that threat credibility is all but necessary for deterrence to succeed also fail to recognize that the assumption that conflict is a mutually worst outcome eliminates the possibility that a player has a credible threat. In consequence, a logical inconsistency arises when players who, by assumption, do not have a rational or credible threat, are then assumed simultaneously to have one. This logical inconsistency is the basis of Achen’s (1987 , 92) insightful observation that “far from leaning too heavily on rational choice postulates, ‘rational deterrence theory’ necessarily assumes that nations are not always self-interestedly rational,” and of Brodie’s (1959 , 293) comment that “for the sake of deterrence before hostilities, the enemy must expect us to be vindictive and irrational if he attacks us.”

To eliminate the contradiction and resolve the paradox of deterrence, Zagare and Kilgour (2000) developed perfect deterrence theory. Unlike decision-theoretic deterrence theory, perfect deterrence theory makes no fixed assumption about the credibility of threats. Rather, it explores the logical implications of a variety of credibility states within the context of a number of closely related, incomplete information game models, the most austere of which is the Rudimentary Asymmetric Deterrence Game. One manifestation of this game is depicted in Figure 1 . Recall that in that game Defender prefers Challenger Wins to Conflict and that, therefore, it could not rationally execute its threat. If one also assumes that information is complete—that is, that Challenger knows Defender’s preferences for sure—then Defender’s threat completely lacks credibility.

Consider now the game in Figure 2 , in which the assumption is that Defender prefers Conflict to Challenger Wins . In this case, it would be rational for Defender to execute its threat and defy Challenger at node 2. And if Challenger knows this for certain, Defender’s threat would be completely credible. It is a straightforward exercise to demonstrate that deterrence will rationally succeed in the Rudimentary Asymmetric Deterrence Game when Defender’s threat is perfectly credible: given that Challenger knows that Defender will (rationally) defy at node 2, Challenger’s node 1 choice is to either cooperate and induce its second most-preferred outcome, the Status Quo , or to defect and induce its least-preferred outcome, Conflict . Clearly, a rational Challenger will choose to cooperate. All of which demonstrates that in the Rudimentary Asymmetric Deterrence Game, deterrence success depends on the credibility, or the lack thereof, of Defender’s threat.

Rudimentary Asymmetric Deterrence Game (Defender’s Threat Is Credible)

Perfect deterrence theory builds on this observation. But rather than assuming that credibility is fixed, it treats credibility as a variable. This is accomplished by assuming incomplete information. Specifically, Zagare and Kilgour assume that each player has probabilistic (rather than certain) knowledge of each other’s preferences. Each player’s credibility, therefore, is determined by the probability that the other believes that it prefers to execute its deterrent threat. 9 In other words, credibility is defined by the perceived rationality of a player’s threat to retaliate.

By relaxing the assumption that threat credibility is fixed and insisting that only rational threats can be executed, Zagare and Kilgour are able to develop an axiomatically distinct theory of deterrence pitched at the level of an individual decision maker. As a result it should be seen not only as distinct from, but also as a theoretical competitor to, decision-theoretic deterrence theory, much the same way that power transition theory stands in relation to structural deterrence theory. But perfect deterrence theory is distinguished from decision-theoretic deterrence theory in other ways as well; not only is its axiomatic base different, but its theoretical characteristics, its propositions about the dynamics of deterrence, and its policy prescriptions are also starkly at odds with those of its mainstream competitor. Table 1 summarizes these differences.

The most important difference concerns the two theories’ assumption about credibility. As noted, decision-theoretic deterrence theorists take credibility as a constant, yet they also assume, inconsistently, that irrational (or noncredible) threats can be executed. Perfect deterrence theory, by contrast, examines the strategic implications of a number of credibility states and insists that only credible threats will be carried out. In fact, perfect deterrence theory’s name derives from its strict adherence to Selten’s (1975) perfectness criterion, which is the basis of almost all solutions to extensive-form games and requires players to make rational choices at every decision node on a game tree. 10

While this difference might appear slight, it has significant empirical implications. Whereas the standard version of the theory concludes that high-cost parity relations are exceedingly stable, perfect deterrence theory finds the opposite. The two theories also differ on the implications of increasing the cost of conflict, either by augmenting the size of a strategic arsenal or by increasing its destructive potential. Nuclear realists like Waltz (1981) see a monotonic relationship between the cost of war and the probability of peace. Thus, since they claim that more is better, they support overkill capabilities that make war more expensive. And, as noted above, those classical deterrence theorists who understand the logical implications of their theories also support the selective dissemination of nuclear weapons (see, e.g., Mearsheimer 1990 , 1993 ; Posen 1993 ; Waltz 1981 ).

By contrast, in perfect deterrence theory, there is a distinct limit to the stabilizing effect of increases in the cost of conflict. Once that point has been reached, the probability of deterrence success does not increase. In consequence, perfect deterrence theory implies support of minimum deterrence policies that rest on a threat that is costly enough to deter an opponent, but that is not so costly as to render the threat itself incredible. In addition, the logic of perfect deterrence theory is inconsistent with policies that promote even the selective proliferation of weapons of mass destruction. 11

Rationality and Deterrence

In the previous section we briefly outlined two strands of classical deterrence theory: structural and decision-theoretic. We have also discussed two of its theoretical competitors: power transition theory and perfect deterrence theory. Thus, it is clear that there is more than one deterrence theory. Yet Morgan (2003) sees only a single theory. And on this score, Morgan is not alone. 12

One reason for Morgan’s view is a common thread that seemingly unites the several variants of modern deterrence theory: the rationality assumption. To be sure, the assumption is ubiquitous, which is one reason that the dominant paradigm is often referred to as rational deterrence theory. Nonetheless, there are important distinctions in the literature in the way this assumption is understood. These fine distinctions lead to very different theoretical structures and are the source of a great deal of pointless debate and criticism ( Zagare 1990 ; see also Quackenbush 2004 ). All of which is to say that “rationality” is an essentially contested concept ( MacIntyre 1973 ), that is, a concept that has no agreed upon definition.

Some theorists equate rationality with near omniscience. Verba’s definition is typical. According to Verba (1961 , 95), a rational actor is one who makes a “cool and clearheaded ends-means calculation” and considers all possible courses of action and carefully weighs the pros and cons of each of them before making a decision. Simon (1976) labels Verba’s and similar definitions of rationality procedural .

The demands of procedural rationality are severe. Clearly few, if any, real-world actors are procedurally rational. When critics of classical deterrence theory, such as Morgan (2003) or Lebow and Stein (1989) , dismiss classical deterrence theory because of this fact, they are most certainly correct. Nonetheless, the procedural definition can serve as a useful benchmark against which actual decisions can be evaluated. Decision-making pathologies and biases could not be recognized, or controlled for, unless this or a similar benchmark was used.

But there is another view of rationality that is commonly used by most formal theorists, including those whom we have labeled decision-theoretic deterrence theorists. According to Luce and Raiffa (1957 , 50), an instrumentally rational actor is one who, when confronted with “two alternatives which give rise to outcomes … will choose the one which yields the more preferred outcome.” Although this definition is less than demanding, it, too, serves a useful purpose. The assumption of instrumental rationality allows a connection to be made between a decision maker’s policy goals and its action choices. In the absence of this simplifying assumption, behavior is inexplicable, which is why Allison (1971) , perhaps unwittingly, uses it to explain state, organizational, and individual decision making during the Cuban missile crisis.

Parenthetically, it should be noted that Schelling’s “rationality of irrationality” stratagem plays on the distinction between procedural and instrumental rationality. What Schelling is saying is that it may benefit a player (i.e., it may be instrumentally rational) to appear to be procedurally irrational. By using two different definitions of rationality, Schelling introduces a logical inconsistency into his theoretical constructs and thereby renders them inscrutable.

To summarize briefly, there are two very different definitions of rational behavior that appear in the deterrence literature. Each serves a useful purpose. Specifications of deterrence that presume procedurally rational behavior, however, are obviously empirically suspect. By contrast, the assumption of instrumental rationality is a useful assumption precisely because it permits the derivation of hypotheses about the conditions associated with either deterrence success or its breakdown. But deterrence theories that merely assume instrumentally rational actors should not be rejected a priori. Rather, they should be judged by the accuracy of their propositions. When these propositions are supported empirically, the assumption of instrumental rationality has served its purpose.

Empirical Testing

While we have focused to this point on the development of deterrence theory, there has also been an extensive empirical literature on deterrence. Empirical studies are important for determining the extent to which deterrence theory helps to understand and explain reality ( Harvey 1998 ). The empirical deterrence literature has largely been divided between case studies and quantitative analyses. 13 A series of debates on case selection, the meaning of deterrence success, and the appropriate theory for testing is important for understanding much of this literature.

Selection of deterrence cases has been a subject of much disagreement, primarily between quantitative and case study researchers. An important symposium published in World Politics in 1989–1990 ( Achen and Snidal 1989 ; George and Smoke 1989 ; Huth and Russett 1990 ; Jervis 1989 ; Lebow and Stein 1989 , 1990) dealt in large part with the proper identification of immediate deterrence cases. However, selection of general deterrence cases has received much less attention. Quackenbush (2010 , 2011b ) argues that the difficult part of general deterrence case selection is not determining who makes deterrent threats (everyone does), but rather what states the threats are directed against. General deterrent threats are directed against any state that might consider an attack, so the key to general deterrence case selection is to identify which states might consider attacking which other states. He argues that the states that might consider an attack on a particular state are those that have the opportunity to fight one another, and uses politically active dyads ( Quackenbush 2006a ) to select cases of general deterrence.

Another concern that has often driven debates between those employing case study ( Lebow and Stein 1989 , 1990) and quantitative ( Huth and Russett 1990 ) methodologies is the determination of deterrence success or failure. However, game-theoretic models of deterrence do not make predictions regarding the success or failure of deterrence, per se; rather, the particular outcome of an interaction is predicted. 14 Furthermore, classification of certain cases as successful deterrence runs into a variety of conceptual and selection bias issues ( Danilovic 2001 ). Therefore, this issue does not pose a problem for empirical tests of game-theoretic models of deterrence. Non-game-theoretic theories of deterrence, however, should be expressed in terms of outcomes, rather than success or failure, in order to avoid this problem.

The third debate we consider here regards the appropriate theory for empirical analysis. The case study literature has focused on in-depth analyses of immediate deterrence in particular crises. These studies have generally not tried to test rational deterrence theory, but rather have criticized game-theoretic analyses of deterrence (e.g., George and Smoke 1974 ; Lebow 1981 , 1984 ; Jervis 1982/1983 ; Jervis, Lebow, and Stein 1985 ; Lebow and Stein 1990 ; Steinbruner 1976 ). Rather than seeking to test a theory of deterrence, they have sought to develop theory from case studies. This is of limited utility, not only because of difficulties of generalizing from a small number of cases, but also because focusing on immediate deterrence is subject to selection effects ( Fearon 2002 ).

The quantitative empirical literature on deterrence (e.g., Danilovic 2002 ; Huth and Russett 1984 , 1988 ; Huth 1988 ; Kugler 1984 ; Russett 1963 , 1967 ; Wu 1990 ) has examined the question of when deterrent threats work using large-N quantitative analysis. The focus of these studies has been almost exclusively on extended-immediate deterrence, with a few older studies (e.g., Huth and Russett 1993 ; Weede 1983 ) addressing general deterrence. Because of selection effects, the findings on when deterrent threats work in immediate deterrence may be misleading. As Fearon (2002 , 15) observes, “hypotheses that are valid for general deterrence should appear exactly reversed if we look at cases of immediate deterrence.” In addition, the quantitative literature has often tested individual hypotheses rather than testing any specific theory of deterrence. Signorino and Tarar (2006) provide an improvement over previous studies by conducting an empirical analysis of extended immediate deterrence using strategic probit, in which the empirical model is embedded within a game-theoretic model.

Quackenbush (2010 , 2011b ) argues that this has led to a divide between formal theories and the quantitative analysis of deterrence and endeavors to bridge the divide. He claims that the key to bridging the divide is to directly test theories of deterrence, and because of its logical consistency and explanatory power, perfect deterrence theory provides the best basis for testing. Quackenbush (2010 , 2011b ) tests the equilibrium outcome predictions of perfect deterrence theory. Since these predictions rely on the actors’ preferences, this requires explicit specification of utility functions for the actors involved. To do this, he employs a modification of the technique—using relative power as a measure for probability of victory and measuring utilities based on similarity of alliance portfolios—pioneered by Bueno de Mesquita and Lalman (1992) . Quackenbush uses binary and multinomial logit methods to examine the prediction of militarized interstate disputes and of particular game outcomes, and the results indicate that the predictions of perfect deterrence theory are generally supported by the empirical record.

Other empirical analyses have evaluated perfect deterrence theory as well. Danilovic (2002) evaluates perfect deterrence theory’s relationship predictions in her quantitative study of extended deterrence. She argues that a state’s inherent credibility—determined in large part by its regional interests—is a far more important predictor of deterrence outcomes than attempts to shore up credibility through the use of commitment strategies recommended by Schelling (1960 , 1966 ) and other classical deterrence theorists. Through her focus on credibility Danilovic (2002) directly addresses a key distinction between perfect and classical deterrence theories. As discussed above, the reason that classical deterrence theorists focus on commitment tactics as ways to shore up credibility is that they assume that all threats are inherently incredible. Zagare and Kilgour (2000) , on the other hand, argue that states’ threats are only credible to the extent that the state actually prefers conflict to backing down. Accordingly, Danilovic’s analysis is an attempt to determine what factors (relative power, regional interests, and democracy) lead states to prefer conflict over backing down.

Perfect deterrence theory has also been applied to the analysis of conflict settlements by Senese and Quackenbush (2003) . Their analysis demonstrates that perfect deterrence theory—through a comparison of the unilateral and generalized mutual deterrence games—makes predictions about the stability of different types of conflict settlements, and these predictions are strongly supported by the empirical record. This is an insight that was not gained through other analyses of the same subject.

Most attempts to test deterrence theory have utilized large-N, quantitative methods. Such analysis is useful because of the generalizable nature of conclusions derived from it. However, case studies would also be useful for future research. Since quantitative analyses demonstrate that perfect deterrence theory is generally supported by the historical record ( Quackenbush 2011a ), it should be no surprise to learn that there is also evidence that the theory can usefully be applied to particular cases. This can be done through the application of the insights of perfect deterrence theory to detailed case studies of particular historical episodes in order to understand these intrinsically interesting events more completely. For example, one study applies perfect deterrence theory to an analysis of the war in Kosovo to answer questions—such as why NATO’s threat of bombing was unable to deter Serbia, and later why Serbia escalated ethnic cleansing once the bombing started—to which others have struggled to find answers ( Quackenbush and Zagare 2006 ). Zagare (2011) tests perfect deterrence theory’s ability to explain the outbreak of World War I through an analytic narrative of the July 1914 crisis. He explains the course of the crisis by explaining a series of important decisions: the formation of the Austro-German alliance in 1879; Germany’s decision to provide Austria-Hungary with a blank check; why Russia, France, and Germany became involved in the dispute between Austria-Hungary and Serbia; and why Britain finally decided to enter the war. Furthermore, his analysis demonstrates that although general war was not sought by any of the actors, the war was no accident.

Theoretical Extensions

As we have seen, perfect deterrence theory is both logically consistent and empirically supported. Nonetheless, further questions regarding the dynamics of deterrence remain. Recent efforts to extend our understanding of deterrence have focused on four primary areas: three-actor games, bargaining, identifying credibility, and deterring terrorism and civil war.

Three-Actor Games

Although direct deterrence deals with two states, extended deterrence deals with a minimum of three. Werner (2000 , 721) outlines the basic logic of extended deterrence: “The attacker must decide whether or not to attack the target, which then must decide whether or not to resist. After observing both the attacker’s and the target’s actions, the third party must decide whether or not to come to the aid of the target if the target has in fact been attacked.” However, standard practice has been to include only two players in models of extended deterrence: the attacker (or challenger) and the defender. Indeed, virtually all analyses of extended deterrence have focused on only two players (e.g., Danilovic 2002 ; Huth 1988 ; Kilgour and Zagare 1994 ; Russett 1963 ; Signorino and Tarar 2006 ; Werner 2000 ; Zagare and Kilgour 1993 ). Thus, although Werner clearly highlights the presence and the choices of the target (as do others), the target’s role in the strategic calculation involved is generally ignored.

Therefore, an important development in deterrence theory has been to explicitly model deterrence situations wherein the choices of the target are strategically salient. Zagare and Kilgour (2003) do so through a Tripartite Crisis Game, which focuses on Protégé’s potential to realign with a more reliable partner should Defender not support her following a challenge. This highlights the importance of the “deterrence versus restraint” dilemma in extended deterrence, wherein Defender has competing interests in having a strong enough commitment to support Protégé so as to deter Challenger, but not in making such a strong commitment that Protégé would be encouraged to act recklessly.

Zagare and Kilgour (2006) extend this analysis to explain British policy in the July crisis leading to the outbreak of World War I. They demonstrate why halfhearted, extended deterrent signals are so often observed in international politics in general, and in Britain’s attempts to deter Germany in 1914 in particular. In so doing, they show that their analysis more fully captures the dynamics of the deterrence versus restraint dilemma than Crawford’s (2003) model of “pivotal deterrence,” which unfortunately is not based on the axiomatic base of perfect deterrence theory.

Quackenbush (2006b) also extends deterrence theory to consider the strategic interactions of all three actors in extended deterrence. He develops a Three-Party Extended Deterrence Game, a formal model that matches the basic informal logic of extended deterrence. This model is the first to explicitly model the simultaneous conduct of extended and direct deterrence identified by Snyder (1961) . Furthermore, the inclusion of all three players in the analysis allows examination of other issues such as the target of a challenge and of alliance reliability.

Quackenbush’s (2006b) analysis indicates that potential challengers look to attack members of unreliable alliances. Furthermore, deterrence is more likely to succeed the more highly Defender and Protégé value a war (bilateral or multilateral) with Challenger, and the less highly they value a concession to Challenger. In addition, Challenger’s increasing utility for the status quo also increases the probability of successful deterrence. And finally, when deterrence fails, the likely target of an attack by Challenger is the more reliable of the allies—in order to keep the unreliable side on the sidelines and prevent a multilateral war.

By including all three actors within game-theoretic models, these studies have significantly improved our understanding of the dynamics of extended deterrence. Certainly further developments in three-actor models are warranted, and they are being developed (e.g., Corbetta 2010 ; Langlois 2012 ; Yuen 2009 ). As Quackenbush (2006b) demonstrates, standard two-party extended deterrence games rely on the often hidden assumption that states always respond to direct challenges. But since this assumption directly contradicts theories of direct deterrence, analyzing all three actors in extended deterrence appears to be a more consistent way of approaching the problem.

Bargaining and Deterrence

Traditional analyses of international relations have modeled decisions as stark choices between two, or sometimes three, alternatives. This is illustrated in the Rudimentary Asymmetric Deterrence Game shown in Figure 2 , which presents choices between “Cooperate” and “Defect” or “Concede” and “Deny.” However, states often have a wide variety of options available to them; for example, rather than just choosing between “attack” or “not attack,” a state could do nothing, partially mobilize troops, fully mobilize, embark on a show of force, launch airstrikes, or even initiate a full-on invasion. This of course provides a much more nuanced menu of options than traditional models would suggest.

The bargaining model of war has been a recent focus of research on international relations (e.g., Fearon 1995 ; Slantchev 2003 ; Wagner 2000 ). Although models vary, they incorporate these nuanced options within the game-theoretic model, making the stakes under consideration endogenous to the model itself. Thus, states choose not only whether to make a demand, attack, and so forth, but also how much to demand, attack, and so forth.

Werner (2000) developed the first model of deterrence to incorporate these endogenous stakes. In her Modified Extended Deterrence Game, the attacker can choose the magnitude of the threat. By modeling the stakes of war as endogenous in this way, Werner is able to identify circumstances under which extended deterrence fails because the attacker deters the third party from intervening.

Langlois and Langlois (2006a , 2006b ) have also examined the relationship between bargaining and deterrence in analyses of direct, asymmetric deterrence. This allows the rivals to bargain over the terms of an alternative status quo. It also shows how war can erupt between two rational states even when there is complete information, contrary to traditional arguments. Similarly, Slantchev (2011) examines how military threats can be employed in the pursuit of political objectives. He focuses on how military threats can establish commitments and communicate intent.

Further analyses integrating such bargaining models within studies of deterrence are likely to continue to be a fruitful avenue for research. Nonetheless, it seems important to recognize the importance of domestic politics and its influence on the demands that states make. For example, Bueno de Mesquita and Lalman (1992) focus on two variants of their International Interaction Game: in the Realpolitik variant, the magnitude of the demand is purely endogenous to the game, whereas in the Domestic variant, the magnitude of the demand is assumed to be determined by domestic political processes and is thus exogenous to the game. Furthermore, they find that the Domestic variant does a much better job of explaining international interactions than the Realpolitik variant.

Identifying Credibility

A third important focus of recent theoretical developments has been on identifying credibility. Perfect deterrence theory demonstrates that credibility is an important determinant of deterrence success. In the presence of complete information, a state’s credibility is simply its preference between fighting and backing down; a state either has a credible threat (i.e., prefers conflict) or does not (i.e., prefers backing down). However, states seldom possess complete information about their opponents.

When there is incomplete information and a state’s preference between fighting and backing down is not known to its opponent, the situation is more complicated. In this case, a state’s credibility is the opponent’s estimate of the probability that it prefers fighting to backing down; thus, credibility varies continuously between 0 and 1 ( Zagare and Kilgour 2000 ). Forming accurate estimates of the opponent’s credibility is complicated by the reality that states have incentives to misrepresent their private information ( Fearon 1995 ). States have incentives to claim that they prefer to fight rather than back down regardless of their actual preference. How can states credibly communicate their commitment to fight in the face of these difficulties?

Two studies in particular have sought to address this question. Sartori (2005) develops a reputational theory of diplomacy whereby defenders acquire reputations for honesty or bluffing depending on whether or not they carry through on their threats to defend against the challenger. She finds that a defender’s reputation for honesty enhances its threat credibility and therefore increases the likelihood of successful deterrence; on the other hand, a reputation for bluffing undermines threat credibility.

In contrast, Press (2004 , 2005 ) proposes a “current calculus” model, which evaluates credibility based on the balance of power and interests at stake and argues that it does a better job of gauging states’ perceptions of their opponents’ credibility than the “past actions” model, which argues that credibility depends on one’s record for keeping or breaking commitments. His focus on assessing the interests at stake to determine credibility is quite reasonable given that credibility deals with a state’s preference between backing down and conflict.

However, it is important to distinguish between credibility and capability; whereas capability is a necessary condition for deterrence success, credibility is not ( Zagare and Kilgour 2000 ). But assessments of the balance of power appear to have more to do with a state’s preference between conflict and the status quo than with a state’s preference between conflict and backing down. Therefore, it appears that Press conflates credibility and capability. For example, he argues that Britain’s threat to defend Poland in 1939 was not credible, in large part because Germany (especially Hitler) misjudged the balance of power. It seems clear that, although it could not be certain, Germany believed that British intervention was likely, and thus the British threat was credible. But as Weinberg (1995 , 91) states, “in August 1939 Hitler preferred to attack Poland as a preliminary to attacking France and England, but he was quite willing to face war with the Western Powers earlier if that was their choice.” In other words, Germany preferred conflict with France and Britain to the status quo; despite being credible, the British threat was not capable.

Deterring Terrorism and Civil War

The final theoretical extensions we consider here focus on how states can deter terrorism and civil war. Civil war (e.g., Collier and Hoeffler 2004 ; Fearon and Laitin 2003 ) and terrorism ( Li 2005 ; Pape 2003 ) have been increasingly prominent topics of study in international relations in recent years. Although less attention has been paid to whether these groups can be deterred, and if so, how deterrence works in this context, studies on both topics are emerging.

Terrorism has been an increasingly popular tactic used by various groups around the world. Most famously, the attacks by Al Qaeda against the World Trade Center and other targets within the United States on September 11, 2001, led many to question why the United States was unable to deter Al Qaeda. More generally, people have questioned whether terrorists can be deterred at all. Trager and Zagorcheva (2005/2006) and Lebovic (2007) examine this issue and conclude that terrorists can be deterred. However, these studies fail to account for both the credibility and the capability of the deterring state’s threat. It would seem that whether or not a terrorist group can be deterred depends on its type. While some terrorist groups certainly can be deterred, others cannot, because they prefer to fight rather than stick with the status quo ( Kang and Kugler 2012 ).

There has also been some attention paid to deterring civil wars. Most prominently, Machain, Morgan, and Regan (2011) have developed a game-theoretic model to examine how states can deter rebel groups from engaging in violence. In doing so, they focus not only on the credibility of the state’s threat to retaliate against rebel attacks, but also on the credibility of its promise to refrain from punishment of groups that do not engage in violence. They show that proportionate retaliation directed only at actual rebels is the most likely to succeed. In contrast, state policies that focus on swift, severe, and disproportionate retaliations are more likely to fail.

Civil war and terrorism are two of the primary threats to international security in the modern age. Analyzing governments’ ability to deter domestic and international rebel groups is an important and natural extension of deterrence theory. Although work in this area is in its very early stages, we are hopeful that continuing studies will improve our understanding not only of government responses to civil war and terrorism, but also of deterrence more broadly.

Policy Debates

There have been a number of debates regarding deterrence policy over the years. A comprehensive review of this large literature on policy debates is beyond the scope of this article. Nonetheless, it is important to address the implications of our examination of deterrence theory and empirical studies for policy. The absence of logical consistency in classical deterrence theory has led to many conflicting prescriptions in the policy literature. Policy recommendations that flow from political imperatives rather than from strategic principles and a consistent axiomatic base are bound to contradict one another. Perfect deterrence theory, by contrast, offers a consistent perspective from which to view the dynamics of deterrence and a clear logic supporting its policy prescriptions. This is, perhaps, its most important feature.

Zagare (2004) and Quackenbush (2011a) provide more complete reviews of perfect deterrence theory’s policy implications regarding topics such as overkill capability, minimum deterrence, proliferation, and missile defense. We review some of the major themes here, focusing on differences in policy conclusions between perfect and classical deterrence theories.

As discussed previously, classical deterrence theory supports both an overkill capability (e.g., Intriligator and Brito, 1984 ) and the selective proliferation of nuclear weapons (e.g., Mearsheimer 1990 ; Waltz 1981 ; and Van Evera 1990/1991 ). Perfect deterrence theory opposes these policies. The logic of perfect deterrence theory demonstrates that there are distinct limits to the stabilizing impact of weapons of mass destruction and that an overkill capability, recommended by many classical deterrence theorists, is just that, overkill ( Zagare and Kilgour 2000 ).

Furthermore, classical deterrence theory opposes both minimum deterrence deployments and significant arms reductions. Perfect deterrence theory is consistent with both these policies. In both classical deterrence theory and perfect deterrence theory, the costs associated with conflict have significant strategic implications. But there are important differences in the conclusions the two theoretical frameworks reach about the impact of increased costs on the likelihood of deterrence success. Classical deterrence theory concludes that deterrence success becomes more and more likely as these costs increase. One reason for this straightforward connection between cost and stability is that most classical deterrence theorists assume fixed preferences: players always prefer an advantage to the status quo, and they always prefer not to execute their deterrent threat (i.e., threats are always incredible). Thus, any increase in the cost of conflict always has the same impact relative to other outcomes.

In perfect deterrence theory, by contrast, the cost of conflict is gauged against two other important strategic variables. The first is the value of the status quo ( Zagare 2004 , 127–128). One consequence of this variable relationship is that, in perfect deterrence theory, there is a minimum cost threshold below which deterrence cannot succeed. This is the point separating threats that are capable from those that are not.

The second reference point is the value of concession. In perfect deterrence theory, the players may, or may not, prefer to concede rather than execute a deterrent threat. This is the reason that there is also a maximum threshold beyond which further increases in the cost of conflict do not contribute to the probability of direct deterrence success. Rather than an overkill capability, then, the logic of perfect deterrence theory is consistent with a policy of minimum deterrence, which rests on a threat that is costly enough to deter an opponent but is not so costly that the threat itself is rendered incredible.

An equally important difference is that there is no simple monotonic relationship in perfect deterrence theory between the cost of conflict and the stability of the status quo, as there is in classical deterrence theory. In perfect deterrence theory, there are circumstances under which an increase in conflict costs will actually undermine a deterrence relationship. More specifically, extended deterrence becomes more and more difficult to maintain as conflict costs rise, simply because defenders become more and more reluctant to respond to an indirect challenge. In perfect deterrence theory, therefore, increased conflict costs can, under some circumstances, be stabilizing, but under others, may have the opposite consequence.

Finally, classical deterrence theorists prescribe coercive bargaining stances based on increasing war costs and inflexible or reckless bargaining tactics. By contrast, perfect deterrence theory suggests that conditionally cooperative policies based on reciprocity are more efficacious. Classical deterrence theory and perfect deterrence theory also differ about negotiating stances and the best way to conduct diplomacy. Recall that decision-theoretic deterrence theorists proffer coercive bargaining tactics that either reduce flexibility or increase an opponent’s conflict costs in order to increase the probability of an opponent’s concession. By contrast, perfect deterrence theory recommends an approach rooted in reciprocity. Conditionally cooperative strategies like “tit-for-tat” that reciprocate both cooperation and noncooperation are associated, both theoretically and empirically, with successful compromise.

In perfect deterrence theory, establishing reciprocity is tantamount to establishing credibility, which in turn makes deterrence more likely. Thus, it is reassuring that in Huth’s (1988) statistical analysis of extended deterrence relationships, firm-but-flexible negotiating styles and tit-for-tat deployments are highly correlated with extended deterrence success. Huth defines a firm-but-flexible diplomatic stance as a signal that the defender is willing to compromise, but not to capitulate. And a tit-for-tat policy involves an actual response in kind during a crisis or mobilization. Thus, the essence of both a firm-but-flexible bargaining approach and a tit-for-tat response to an actual provocation is reciprocity, the norm that signals credibility when promised or threatened and demonstrates it when practiced. There is, as well, a large empirical literature that is consistent not only with Huth’s findings but also with the theoretical expectations of perfect deterrence theory about the pervasiveness of reciprocal behavior in interstate interactions. This evidence attests to perfect deterrence theory’s explanatory and predictive power. By contrast, this widely observed norm is difficult, if not impossible, for classical deterrence theorists to explain.

Conclusions

Thirty years ago philosopher Anthony Kenny (1985 , ix) asserted that deterrence was “the key concept for the understanding of the strategy and diplomacy of the age.” Obviously, much has transpired since Kenny made his claim. The end of the Cold War was followed by conflicts in the 1990s in Iraq, the former Yugoslavia, between India and Pakistan, and elsewhere. Further, the 9/11 terrorist attacks ushered in a new “global war on terror,” as the United States and allies toppled regimes and fought counterinsurgency campaigns in Afghanistan and Iraq. The second decade of the twenty-first century witnessed civil wars and conflict in Libya, Syria, Ukraine, and elsewhere.

As these events unfolded, the significance of deterrence, as both a concept and a policy, came under intense attack. As a concept it was seen as largely irrelevant to the post–Cold War era, or, as Colin Gray (2003 , vi) put it, deterrence appeared to be in “semiretirement.” And as a policy, it was judged “obsolete” ( Krauthammer 2002 ). Many strategic thinkers concluded that deterrence was an ineffectual strategem against terrorists and other “undeterrables” ( Friedman 2002 ). Deterrence was also thought to be an inappropriate policy toward risk takers like Saddam Hussein, who operate in a world of half-truths, distorted intelligence, and incomplete information ( Pollack 2002 ). In Washington, the strategic doctrine of “preemption” was all the rage. To all the world it appeared that deterrence, like God in the 1960s, was probably dead. At a minimum, it was seen to be on life support. The situation appeared so bleak that the New York Times (2002) felt compelled to write an editorial “in defense of deterrence.”

But the news of deterrence’s demise was premature. Judging from the academic literature, this would certainly appear to be the case. Books and articles about deterrence continue to be published by the best academic presses and the major security studies journals. Among the significant book-length manuscripts on deterrence that have appeared since the turn of the century are Crawford (2003) ; Danilovic (2002) ; Freedman (2004) ; Gray (2003) ; Morgan (2003) ; Paul, Morgan, and Wirtz (2009) ; Payne (2001) ; Quackenbush (2011b) ; Sartori (2005) ; and Zagare (2011) . Taken as a unit, these works demonstrate that the core debates about deterrence’s theoretical underpinnings, its empirical robustness, its conceptual clarity, and its policy relevance continue.

All of which is to say that deterrence, and the theories that seek to understand it, stand at the very center of the discipline of international politics. Thus, it should not be surprising at all that despite suggestions to the contrary, research on deterrence is thriving, or that this scholarship is unlikely to go away now or in the foreseeable future. Our analyses of logic and evidence show that perfect deterrence theory provides the best available explanation of deterrence. Given its logical inconsistency and empirical inaccuracy, classical deterrence theory should be set aside. In our opinion, future theoretical developments, empirical analysis, and policy assessments are better served by using perfect deterrence theory as their foundation.

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Zagare, Frank C. , and D. Marc Kilgour . 2000 . Perfect Deterrence . Cambridge, UK: Cambridge University Press.

Zagare, Frank C. , and D. Marc Kilgour . 2003 . “ Alignment Patterns, Crisis Bargaining, and Extended Deterrence. ” International Studies Quarterly 47 (4): 587–615.

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See also Hastings (2013 , 78).

The charge was officially denied by Russian officials shortly after the publication of Sudoplatov’s book.

Classical deterrence theory is also sometimes referred to as rational deterrence theory. However, there are other theories of deterrence based on rational choice that would therefore seem to fall within the umbrella of rational deterrence theory.

For a formal model that succinctly captures the interplay between relative capability and the cost of conflict in the context of an arms race, see Intriligator and Brito (1984) . The deductions of this model are entirely consistent with the two major propositions of structural deterrence theory as well as with its policy proposals.

Not all structural deterrence theorists place a high value on logical consistency (see, e.g., Walt 1999 ), which perhaps explains why not all structural deterrence theorists endorse proliferation policies.

For a closely related theoretical construct, see Gilpin (1981) .

For example, in power transition theory, great power conflicts require both a dissatisfied challenger and a power transition. But as Zagare and Kilgour (2000 , ch. 2) show, while these two conditions may be necessary for a major power war to occur, they are not sufficient. Under complete information, wars never occur at all. And when, more likely, information is incomplete, wars occur only under certain specific conditions.

See also Hamilton and Herwig (2003) ; Mulligan (2010) ; Clark (2012) ; McMeekin (2013) ; and Hastings (2013) .

In the Rudimentary Asymmetric Deterrence Game, Defender alone has a threat that it may or may not prefer to execute. In more elaborate models, Challenger may also possess a threat to retaliate. For the details, see Zagare and Kilgour (2000) .

Most decision-theoretic deterrence theorists rely on Nash’s criterion, which is less demanding, to resolve the paradox. Powell (1987) and Nalebuff (1986) are exceptions. A Nash equilibrium, which is the standard measure of rational play in strategic-form games, is any outcome that offers no player an opportunity to induce a better outcome by unilaterally switching to another strategy. Nash equilibria, however, may be based on incredible threats (i.e., on threats of irrational choice).

Much the same can be said of power transition theory. For a trenchant counterpoint to Waltz’s (2012) argument that a nuclear armed Iran would be a stabilizing force in the Middle East, see Kugler (2012) .

See Quackenbush (2011a) for a thorough discussion of this point.

Levy (1988) and Huth (1999) provide reviews of the empirical literature on deterrence.

For example, in the Rudimentary Asymmetric Deterrence Game (figure 2 ), the only rational outcome is Status Quo if Challenger prefers Status Quo to Challenger Wins . Although Challenger’s decision to not challenge the status quo in this case is not really “successful deterrence,” it is predicted by perfect deterrence theory.

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Research Methods in International Relations

• Christopher Lamont - Tokyo International University
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The only guide to conducting research in International Relations. Covering the full breadth of methods in IR with unrivalled clarity, this best-selling textbook takes you through the entire process of doing research, from honing your question to writing up the dissertation. The engaging and jargon-free style demystifies the process of doing research, whilst helping you develop a comprehensive understanding of the strengths and limitations of different methods and methodologies. This second edition comes with new chapters on conducting interviews and discourse analysis, as well as expanded coverage of qualitative and quantitative methods. Packed with examples, it explores the breadth of IR research today, from the long-lasting impact of colonialism to migration policy; climate change negotiations to international aid. Covering the most cutting-edge methodological developments, including critical realism, feminist, and postcolonial approaches, it helps you understand and apply research methods in world politics.

This practical introduction is essential reading for anyone setting out on their International Relations research project for the first time, at undergraduate and postgraduate levels.

Christopher Lamont is Assistant Dean of E-Track Programs and Associate Professor of International Relations at Tokyo International University, Japan .

A superb primer for those embarking on research in international relations.  The text outlines a range of approaches in a practical fashion, with references to the latest developments in theory as well as current affairs. Readers are taken through complex ideas about methods, the philosophy of knowledge and ethics with clarity, insight, and a nuanced appreciation of the value of different ways of going about inquiry in this field. Destined to become the 'go to' manual for existing IR researchers as well as the first book to recommend for those starting a PhD.

This text is an accessible introduction to International Relations research and is particularly well-suited to undergraduates embarking on their first projects. It covers the entirety of the research process, from devising questions to writing-up findings. The new chapters on interviews and discourse analysis are great additions to this second edition.

This will support learners in the research unit, there are three scopes within the research module. Learners doing a research topic will have this on their reading list for Research Skill in International Relations.

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Research Methods in Politics and International Relations

• Christopher Lamont - Tokyo International University
• Mieczyslaw P. Boduszynski - Pomona College, USA
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This is the perfect guide to conducting a research project in Politics and International Relations. From formulating a research question and conducting a literature review to writing up and disseminating your work, this book guides you through the research process from start to finish.

-        Is focused specifically on research methods in Politics and IR

-        Introduces the central methodological debates in a clear, accessible style

-        Considers the key questions of ethics and research design

-        Covers both qualitative and quantitative approaches

-        Shows you how to choose and implement the right methods in your own project

The book features two example research projects – one from Politics, one from International Relations– that appear periodically throughout the book to show you how real research looks at each stage of the process. Packed full of engaging examples, it provides you with all you need to know to coordinate your own research project in Politics and International Relations.

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There’s no better learning experience for political science students than carrying out an original research project. But the task can be daunting for students as well as instructors.  Research Methods in Politics and International Relations  is an excellent new resource that will be a useful companion as students set out on this endeavor.  Boduszynski and Lamont’s book is methodologically inclusive and touches on important subjects that are often overlooked, such as research ethics and publishing.

Research Methods in Politics & International Relations is a highly useful, engaging, and accessible methods textbook anchored in concise and compelling chapters and clear explanations of key dimensions of qualitative and quantitative research processes. Moreover, the book provides undergraduates with an in-depth understanding of how to design and carry out different types of research projects, ranging from research papers, capstone research projects, and senior dissertations.

Research training is more important than ever for students of Politics and International Relations at all levels. Lamont and Boduszynski provide a comprehensive, pluralist and accessible guide to the research process and the challenges and dilemmas it entails, a great resource for teachers and students alike.

Boduszynski and Lamont’s new textbook breaks new ground in promoting a comprehensive introduction to research methods in politics and international relations. I especially appreciated the unique discussion of research ethics, which provides an opportunity to reflect on the broader significance of one’s research as well as the importance of protecting human subjects. The text wholeheartedly embraces the notion of methodological pluralism, giving equal voice to a range of qualitative and quantitative methods. It does this while avoiding the divisive debates about whether some approaches are superior to others. The progression of chapters also usefully mirrors the research process, from exploring topics to writing and publishing.

“Writing Up”, Chapter 11, is an excellent resource. This is a practical chapter that presents a road map to essay writing, an outline for a thesis, and a check list for the nervous student. Beautifully, the authors remind us that "academic writing, reflecting the social phenomena that we study, is not a book reviews linear process” (p. 167), while continuing to instruct us on the contents of an introduction, the importance of the thesis or main argument, the best ways to present data and empirical analysis, and the elements all good conclusions must contain. Used in the way it was intended, as a guide to writing, a reference for further reading, and as a plan for research design, Research Methods in Politics and International Relations has the potential to improve the readability of student work and provide a template for lecturers to guide undergraduates and postgraduates alike through the minefield of research. 

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