This volume is dedicated to J. David Singer, and it is designed to be a collective reflection on Singer's work and the Correlates of War (COW) research program that he initiated more than 40 years ago. It accomplishes much more than simply revisiting or lauding previous COW research, however. As Paul Diehl (p. xi) notes in the preface, the “collection is one in which leading scholars look back in order to move the study of international relations forward.” Because it is so successful in this challenging task, the volume deserves a wide audience.

The first two chapters use novel approaches to further our understanding of the evolution of war and militarized disputes over the past two centuries. In the first chapter, Claudio Cioffi-Revilla and Manus Midlarsky demonstrate that the magnitude of the most lethal international and civil wars is amenable to modeling with statistical power laws. This potent, systemic model sheds light on an important characteristic of war without delving into state- or individual-level particulars. In Chapter 2, Monica Lagazio and Bruce Russett use the relatively novel and flexible method of neural network analysis to confirm that the variables central to the “Kantian peace” hold across both the pre–Cold War and the Cold War periods.

The next three chapters examine national and subnational explanations of war. Building from one of Singer's widely read articles, Zeev Maoz in Chapter 3 compares world leaders' presumptions about the causes of war and peace, gleaned from speeches at the United Nations Millenium Summit, to the empirical record of conflict behavior. It is somewhat comforting that he finds more convergence between leaders' assumptions and the actual record than Singer did three decades ago. In Chapter 4, Bruce Bueno de Mesquita and James Lee Ray provide a lucid rendering of the institutional approach to conflict behavior and then use it to demonstrate the robustness of the democratic peace in comparison to the autocratic peace. Volker Krause builds on earlier COW-related work on the relationship that alliances and defense expenditures have with conflict outcomes in Chapter 5. His results suggest that only a combination of allied and actor capabilities explain war success.

The final four chapters examine dyadic and interactive explanations. In Chapter 6, Douglas Lemke and Patrick Regan return to Singer's inter–nation influence model to advance Regan's past work on interventions into civil wars. Their innovative use of this largely overlooked theoretical approach allows them to demonstrate not only that outside interventions supporting rebels tend to be longer than those supporting target governments, but also that they are bloodier and use higher levels of force. In Chapter 7, Errol Henderson dissects Singer's skepticism about the democratic peace and provides empirical evidence that seems to support such skepticism. Paul Senese and John Vasquez build on earlier COW research on alliances and war in Chapter 8. They show that territorial revisionist policies and alliances increased the likelihood of disputes escalating to war in the pre–Cold War period and that, under certain conditions, these two explanatory variables can interact to produce war. In the concluding chapter, Daniel Geller provides a compelling discussion of the epistemology that has guided much of the COW research program and an extremely useful summary of the knowledge the program has generated on war onset and severity.

As should be apparent, this is a theoretically and methodologically diverse volume. The different conclusions that Lagazio and Russett (chap. 2) and Henderson (chap. 7) reach on the democratic peace are one example of this diversity. When one considers the longer view the volume frequently takes, however, these conflicting outcomes are also suggestive of the knowledge that is generated from clashing perspectives. Moreover, as Diehl implies in the preface, the variety of approaches that are included in the collection are a reflection of the COW research program more generally. It has grown into a vibrant, varied community of scholars developing and testing a wide range of middle-range theories. The advances the field has made in understanding international conflict are in no small part due to the efforts of members of this community and the rich array of theoretical and methodological approaches they have pursued.

The collection also underscores an often overlooked aspect of the COW research program: its policy relevance. Most of the chapters are explicit on how their findings can inform policy, with the Cioffi-Revilla and Midlarsky (chap. 2), Maoz (chap. 3), Lemke and Regan (chap. 6), and Geller (chap. 9) contributions being notable in this regard. Geller also correctly observes that the knowledge being imparted to the academic and policy communities is increasingly subtle and nuanced. Contemporary empirical research appreciates that complex phenomena like war are the result of multiple, interacting conditions that can develop along numerous distinct causal paths.

Taken together, this collection offers a trove of new or reformulated theories and methodologies that will further invigorate the quantitative conflict literature. Chapter 3 by Maoz and Chapter 6 by Lemke and Regan are illustrative. Both chapters convincingly revisit an underutilized theory or approach. In doing so, they may prompt scholars to reconsider a range of potentially useful theoretical approaches developed in association with the COW program over the past four decades.

The volume does have minor flaws. Some chapters overlook important prior research. For example, Maoz's discussion of the impact of outside intervention on civil war duration might have incorporated Regan's work on the subject (such as Patrick Regan, Civil Wars and Foreign Powers, 2000). Bueno de Mesquita and Ray's contribution might have addressed previous findings that contradict their conclusion, particularly those of Mark Peceny and Caroline Beer, with Shannon Sanchez-Terry (“Dictatorial Peace?” American Political Science Review 96 [March 2002]: 15–27). The chapters are also inconsistent in their treatment of selection effects, which raises questions about analyses that do not control for them.

Overall, though, The Scourge of War is an impressive volume that stands as a testament to the vitality of the COW research program. It is essential reading for those interested in the systematic study of international conflict, and it will likely become a staple in graduate courses on the subject.