Terrorism studies is a famously interdisciplinary field. By most accounts, the field’s dominant discipline is political science, followed closely by psychology, then by other disciplines such as criminology, sociology and economics. Some see this interdisciplinary nature as a strength, some see it as a weakness.

But what form does this interdisciplinarity take? Most people in the field would agree that the situation is not one of disciplinary siloes where, for example, the psychologists and criminologists never talk to each other. But this does not mean there is uniform interdisciplinarity, with each discipline engaging equally with others.

Instead, different parts of disciplines appear to cluster together in specific ways, but I have rarely seen this explored. Several scholars have mapped the prevalence of different disciplines within the field, but I’m not aware of any work mapping how the disciplines interact with each other.

I want to propose a way understand the relationship between different disciplines that engage with terrorism studies, for two purposes. One purpose is to invite critical feedback from other scholars. The other is to help new students and early career researchers make sense of the field.

I would suggest that there are three core interdisciplinary clusters in terrorism studies:

1. Quantitative political science and economics
2. Qualitative and mixed methods political science, history and macro-sociology
3. Psychology, criminology and micro-sociology

The clusters are loosely based on the following criteria:

• Whether terrorism scholars within particular disciplines or parts of disciplines tend to collaborate with each other.
• Whether works that aggregate components of the field, such as review articles, edited volumes, or large-scale projects, tend to repeatedly group together particular disciplines or parts of disciplines.
• Whether some journals or outlets attract contributions from a particular combination of disciplines or parts of disciplines.

My judgements about what fits what criteria are based on my anecdotal impressions, and not from any formal or transparent method. So, I am keen to hear from other scholars of terrorism about whether this matches, or clashes with, their own way of mapping the field. I am particularly unsure about the distinction I make between macro-sociology and micro-sociology.

Each of the three clusters is described below with some representative examples.

1. Quantitative political science and economics

Quantitative political science includes statistical approaches, formal/mathematical modelling approaches, and computational modelling approaches (although this last one is quite rare in terrorism studies). The discipline of economics is commonly characterised by these approaches, which were imported into political science, particularly in the United States. So US-based researchers are heavily represented in this cluster of terrorism studies.

Representative examples include Jacob Shapiro’s review article, Terrorist Decision-Making: Insights from Economics and Political Science, Todd Sandler’s The Analytical Study of Terrorism: Taking Stock, and Joseph Young and Michael Findlay’s Promise and Pitfalls of Terrorism Research. Most terrorism articles in highly ranked political science journals like The Journal of Peace Research or The Journal of Conflict Resolution would also sit within this cluster.

2. Qualitative and mixed methods political science, history and macro-sociology

The political science component of this cluster is far more qualitative than the previous one. It does not avoid quantitative methods but tends to use them to complement qualitative approaches. Historical approaches would be self-explanatory, and there has been a compelling historical turn in the field. By macro-sociology, an imperfect term, I am referring to social movement theory approaches and other accounts that tie terrorism into large-scale social processes.

3. Qualitative and mixed methods political science includes the highly formalised approaches common in the United States  as well as the more informal approaches that characterise much of terrorism studies.

Representative examples include Erica Chenoweth, Richard English, Andreas Gofas and Stathis N. Kalyvas’s edited volume The Oxford Handbook of Terrorism. Erica Chenoweth and Pauline L. Moore’s excellent and under-rated book, The Politics of Terror, mostly fits within this cluster but less neatly given the book’s sections of the psychological approach to terrorism. It would be fair to say that a lot of the literature that describes itself as jihadism studies would also sit in this cluster, and I would guess the same for articles that tend to be published in Studies in Conflict and Terrorism. This cluster would also include many parts of terrorism studies that overlap with other fields such as civil war studies, area studies and maybe communications studies (as well as strategic studies, but that overlap is surprisingly rare).

3. Psychology, criminology and micro-sociology

Psychology and criminology would be self-explanatory. By micro-sociology I am referring to sociological accounts that focus on the individual or perhaps group level, such as Lorne Dawson and Amarnath Amarasingam’s adoption of sociology of religion approaches to Islamic State foreign fighters.

Representative examples include Lara A. Frumkin, John F. Morrison and Andrew Silke’s edited volume A Research Agenda for Terrorism Studies, although this is not a perfect fit. The editors are criminologists and psychologists but several chapters draw on other disciplines. This cluster would also include most of the threat assessment literature on terrorism, such as the various validation studies of TRAP-18, and the risk assessment literature on terrorism, such as Michael Wolfowicz, Yael Litmanovitz, David Weisburd, Badi Hasisi’s review article Cognitive and behavioral radicalization: A systematic review of the putative risk and protective factors. Other representative examples include many publications that came out of the Grievance Project and many projects based on the Profiles of Individual Radicalization in the United States (PIRUS) dataset.

What might all this tell us? Essentially, that there are disciplinary divides within terrorism studies, but they don’t take the form of a silo for each discipline. Instead, the key divides are between three distinct interdisciplinary clusters. The result is that review articles and edited volumes often fall neatly into one these clusters rather than encompassing the entire field.

That is not a bad thing; it’s an unwieldy field and trying to encompass it all would be formidable. This edited volume by Diego Muro and Tim Wilson looks like a great effort to do so, though I haven’t read it yet. Bart Schuurman’s review articles are extremely comprehensive, covering all the main journals (Terrorism and Political Violence, Studies in Conflict and Terrorism, Perspectives on Terrorism, the Combating Terrorism Center Sentinel, Critical Studies on Terrorism, Dynamics of Asymmetric Conflict, Behavioral Sciences of Terrorism and Political Aggression, the Journal of Terrorism Research  and the Journal for Deradicalization). Yet my impression is that these terrorism journals are most likely to include work from the second and third cluster. Work from the first cluster is more likely to be published in non-terrorism journals (particularly journals from mainstream political science and economics, security studies and conflict studies), hence the prominence of outlets like The Journal of Conflict Resolution in Brian J. Phillips’ wide-ranging review article across thousands of journals.

Also, none of this means there are not further distinctions within each cluster. For example, psychological and criminological approaches make explicit efforts to consolidate their own disciplinary strength, and at times protect their turf, while nonetheless routinely cooperating with each other. Historical approaches similarly seek to differentiate themselves while still cross-pollinating with some political science and sociological approaches.

There are also further twists within each cluster. Much of the qualitative and mixed methods political science research on terrorism, in the second cluster, could be considered within the sub-discipline of comparative politics. However, terrorism scholars rarely explicitly situate themselves within comparative politics. This contrasts with the political science research on civil war studies, which tends to explicitly situate itself in comparative politics. I’ve noted before that terrorism studies and civil war studies have increasingly been working together over the past decade. This can be built on, in part by situating more of terrorism studies in comparative politics. However, as Thomas Hegghammer has contended, one downside of the field’s interdisciplinarity is that terrorism scholars risk being unaware of the broader debates and developments within their specific disciplines. The study of revolution is likewise a thriving sub-field of comparative politics that terrorism studies could learn from.

These divides between interdisciplinary clusters are not theoretical divides. For example you can broadly find principal-agent theory approaches in both the first cluster and the second cluster, but they take radically different forms. You can similarly find social network analysis in multiple clusters, taking a more mathematical form in the first and third clusters and a more qualitative form (but still somewhat mathematical) in the second.

These divides between the clusters are also not political divides (though these certainly exist in the field). I would think that the work of many scholars from the Critical Terrorism Studies tradition would fit into the second cluster, qualitative and mixed methods political science, history and macro-sociology (though there are debates over whether the interpretivist approaches, often used by critical theorists, should be lumped under the qualitative label). A fair amount could also fit under the third cluster of psychology, criminology and micro-sociology (critical criminology being a prominent sub-field), but I assume that very little would fit into the first cluster of quantitative political science and economics. However, there is an interesting argument that the interpretivist approaches often used by critical theorists are perfectly compatible with statistical, mathematical and computation methods despite the gulf between them in practice.

Another issue is that a lot of critical theory scholars would be sociologists, and I worry that by distinguishing between macro-sociology and micro-sociology I’ve artificially left no clear cluster for quite a number of such scholars. Potentially worsening this problem, I have completely left several relevant disciplines out of the three clusters above. For example, it is not clear in which cluster anthropological approaches to terrorism (which seem to be more common in the Critical Terrorism Studies tradition) would belong.

Beyond these three core clusters, the field appears to be more siloed. For example, legal studies of terrorism appear to be their own distinct area, as are computer science approaches.

But my impression remains that these three clusters appear to be the central disciplinary divides in terrorism studies. In the absence of an exercise to formally map the field’s interdisciplinary clusters, I’m curious to know if other scholars of terrorism have the same impression.