Deterrence is a national security strategy aimed at persuading an adversary that the costs of attacking exceed the benefits. During the Cold War, U.S. leaders sought to deter an attack by the Soviet Union on the United States or its allies in Europe by threatening to respond with nuclear weapons. The United States worked hard to maintain a powerful nuclear deterrent and to convince the Soviet Union that it would actually initiate nuclear war if push came to shove, but most analysts came to believe that these efforts were unnecessary: The mere possibility of a catastrophic nuclear exchange produced robust deterrence.

Complex Deterrence seeks to assess the relevance of deterrence in contemporary international politics. The basic premise is that the world today is much more complicated than it was during the Cold War; scholars and policymakers should thus deviate from that era's “straitjacket conceptions” (p. 20) of deterrence and, instead, understand the nature of complex deterrence relationships that will dominate the globalized world of the twenty-first century. Deterrence is more complex today because of the increased importance of nonstate actors, international organizations, and domestic and transnational audiences; the emergence of significant power asymmetries, particularly between the United States and all other countries; and ambiguity about the motives of many potential adversaries. Perhaps no problem better captures the greater complexity of deterrence today than the challenge of deterring seemingly nonrational, suicidal terrorists committed to pursuing highly intangible goals.

The book outlines five types of deterrence relationships in the contemporary era that warrant new scholarly thinking and policy approaches: deterrence among great powers; deterrence among new nuclear states; deterrence and extended deterrence involving nuclear great powers and regional powers armed with chemical, biological, and nuclear weapons; deterrence between nuclear states and nonstate actors; and deterrence by collective actors. Each of these topics is covered in one or more chapters by more than a dozen prominent scholars in security studies or related fields.

The first two sections of the edited volume (the introduction by T. V. Paul and chapters by Jeffrey Knopf and Janice Gross Stein) are largely conceptual and succeed in hammering home the point that deterrence is, well, complicated. Students of nuclear deterrence theory typically learn that a successful deterrence strategy depends primarily on the capability to inflict costs on a potential attacker, the credibility of threats to inflict such costs in the event of attack, and the communication of those threats to the potential attacker. But these authors argue that the theory and practice of deterrence depends on all sorts of additional factors, such as the rationality of actors, the historical context, the availability of alternative strategies, the extent of shared norms, and so forth. Paul discusses how new global conditions generate a list of research questions, Knopf calls for a broad concept of deterrence that does not limit the concept to military capabilities or goals, and Stein uses findings from neuroscience and cognitive psychology to critique the impoverished notion of rationality at the heart of deterrence theory.

The third, fourth, and fifth sections of the book tackle the topics of deterrence and nonstate actors, deterrence and smaller powers, and deterrence and major powers, respectively. Emanuel Adler offers a social constructivist take on the problem of deterring asymmetrically weaker adversaries; Paul Kapur explores whether states can deter terrorists from using nuclear weapons; Robert Jervis concentrates on the debate over deterring rogue states; Patrick Morgan discusses the challenge of collective-actor deterrence (that is, deterrence as practiced by the United Nations or other international bodies); Dinshaw Mistry explores the effect of nuclear weapons on the India-Pakistan relationship; Ivan Arreguìn-Toft explains how weak actors deter strong ones; Frank Harvey and Patrick James present a case study of deterrence in Iraq from 1991 to 2003; and Morgan and Paul, Timothy Crawford, and Michel Fortmann and Stèfanie von Hlatky discuss different dimensions of the impact of contemporary change and complexity on great power deterrence behavior. James Wirtz summarizes the central themes of the volume in a concluding chapter.

Any single chapter in Complex Deterrence has something to offer for interested readers, but the book's overall contribution to international relations theory, security studies, and national security policymaking is harder to pin down. For one thing, there may not be much more to contribute beyond the general point that “it's complicated.” More specifically, several essays fall short in terms of offering either new theoretical generalizations about deterrence behavior or concrete policy recommendations for statecraft. For example, one author concludes that the United States and other Western powers could better avoid conflict with Islamic terrorists and the Iranian regime if they abandoned the self-defeating “deterrence trap” and, instead, pursued “common knowledge–creating diplomacy” to learn more about each others' worldviews, fears, and emotions. Even if one agreed that the cause or solution to these conflicts has something to do with social misunderstanding, the author provides no guidance for how such diplomacy should be undertaken, other than to act with great care “through bilateral and multilateral diplomacy—perhaps with the help of ‘epistemic communities’” (p. 103).

Ironically, the very best essays in the book offer clear and simple analyses about the topics that have supposedly rendered modern deterrence so complex: terrorists, rogue states, and security relations among smaller nuclear powers. Kapur's exemplary chapter, “Deterring Nuclear Terrorists,” makes a compelling argument that states can devise deterrence strategies to protect themselves against nuclear terrorism. One strategy aims to make the acquisition and use of nuclear weapons so difficult that terrorists would not even attempt it; the other seeks to make nuclear attacks so costly for terrorists that they would decide not to acquire and use nuclear weapons, even if they were physically capable of doing so. Further, Kapur identifies types of terrorist groups and ranks their susceptibility to these deterrent strategies, illustrates his argument by contrasting the potential effectiveness of these strategies against Al Qaeda and a group more similar to Aum Shinrikyo, and concludes with a discussion of specific policy implications and their potential drawbacks.

Similarly, the chapter by Jervis, “Deterrence, Rogue States, and the U.S. Policy,” takes a seemingly new and complex challenge and dispels much of the unfounded pessimism about the utility of the deterrence framework for addressing it. Some members of the George W. Bush administration frequently argued that rogue states—that is, those states seen as unpredictable, repressive, international law-breaking, and expressly hostile to American interests—are especially hard to deter. Without minimizing the difficulty of deterrence, Jervis adeptly shows how this skepticism rests on questionable assumptions, logical inconsistencies, and weak empirical evidence. Of course, skepticism about deterring unsavory regimes that remain interested in acquiring nuclear weapons has outlasted the Bush administration, and so his chapter should remain a useful corrective.

Finally, Mistry's chapter, “Complexity of Deterrence among New Nuclear States: The India-Pakistan Case,” does an excellent job of comparing the unfolding story of deterrence in South Asia today with deterrence between the superpowers during the Cold War—noting that both cases show complexity as well as recognizable patterns of behavior.

In the end, it is worth asking whether the basics of nuclear deterrence—in theory or practice—are as complex or different today as they were during the Cold War. Many of the contributing authors seem ambivalent about this question, even where one would expect common agreement. Morgan and Paul suggest that nuclear deterrence is largely irrelevant among the major powers today, a view echoed in places throughout the book. Yet, Fortmann and von Hlatky correctly note that America's embrace of potentially transformative technologies at both the conventional and nuclear level might have huge consequences for great power relations, including the fostering of arms races, a blurring of the distinction between conventional and nuclear weapons, a lowering of the nuclear-use threshold, the exacerbation of regional hostilities, and (via the reaction of other major powers) the undermining of America's nuclear umbrella to allies abroad. To paraphrase Clausewitz, everything about nuclear deterrence is simple. But the simplest thing is difficult.