In this ambitious volume, editors Kelly M. Greenhill and Peter Krause offer a new look at one of the international system’s most enduring forms of behavior: coercion. The book is divided into five sections comprising 15 different chapters on various topics related to coercion, plus an introduction and conclusion. Part I serves as the “Primer,” and Part II concerns theories of “Coercion in an Asymmetric World,”—attempts by strong states to coerce the weak. The essays in Part III consider nonstate actors, while Part IV surveys “Domains and Instruments Other Than Force.” Part V focuses on nuclear weapons. The foundational scholarship on coercion arose during the Cold War, with an emphasis on nuclear deterrence and bipolar competition. Coercion is intended to apply these ideas to the new challenges and actors of the twenty-first century. Thus, we find chapters discussing not only nonstate actors but also cyberwarfare, smart sanctions, and unmanned aerial vehicles, in addition to more “traditional” topics like nuclear weapons.

The essays are well executed, and the topics they cover are both varied and timely. The volume is most successful where the authors directly engage with the core concepts of compellence and deterrence. Todd Sechser’s superb chapter, “A Bargaining Theory of Coercion,” presents a basic and elegant game-theoretic model of coercive diplomacy that yields a rather counterintuitive finding: the more powerful a coercer becomes, the more likely its threats are to fail (p. 71). In a two-round competition, strong coercers are more willing to run the risk of war by making large demands of the target state in the opening round, and thus their threats are more likely to fail. In a similar vein, Jon R. Lindsay and Erik Gartzke apply the core concepts of coercion theory in their chapter, “Coercion through Cyberspace.” They argue convincingly that cyber competition bears many similarities to the classic “stability–instability paradox” that arose from nuclear theory in the 1960s. Keren E. Fraiman introduces the concept of “transitive compellence” in her chapter (“Underestimating Weak States and State Sponsors”), wherein a state tries to compel another state to take action against a violent nonstate actor operating within its borders. This is a timely and useful extension of standard compellence theory.

Readers familiar with classic works like those by Alexander George and William Simons (The Limits of Coercive Diplomacy, 1994) or Robert Art and Patrick Cronin (The United States and Coercive Diplomacy, 2003) may miss the wealth of detailed case analysis presented in those books. Given that Coercion packs 15 separate essays into well fewer than four hundred pages, this was probably a necessary sacrifice. Case studies remain particularly valuable to the study of coercion, however, because success or failure hinges on the beliefs that the target holds, and the way in which the coercer’s threats or inducements influence those beliefs. The question “Did our threat successfully deter the targeted state?” can only be answered accurately with detailed and intimate knowledge of the target’s decision making and calculations. Thus, Austin Long argues convincingly in his chapter, “Intelligence and Coercion,” that intelligence is a neglected but vital element of coercion, both for scholars studying the phenomenon and for policymakers attempting to evaluate the effectiveness of their policies.

Although this volume boasts several strong chapters, it suffers from the failure to define its subject in a useful way. The first chapter—“Primer” by Robert J. Art and Greenhill—defines coercion as “the ability to get an actor . . . to do something it does not want to do” (p. 4). This is inconsistent not only with how coercion is defined by the foundational works in the field but also with how the term is employed elsewhere in the volume (with the exception of Greenhill’s chapter). Defined this way, “coercion” is a quality that an actor possesses. It is very similar to Robert Dahl’s classic definition of power (“The Concept of Power,” Behavioral Science, 2(3), 1957): “A has power over B to the extent that he can get B to do something that B would not otherwise do.”

Defining the key term in this unusual way obscures the distinction between persuasion and force that is at the heart of coercion. Coercion is a process by which one actor employs threats or promises to convince another actor to change its behavior, either now or in the future. It is distinguished from the use of brute force by the key mechanism of persuasion. Although coercive diplomacy may involve the actual use of limited force to signal the target state, the use of such limited force is not primarily intended to degrade the physical capabilities of the target.

The overly broad definition of coercion presented in the first chapter lends the volume an uneven quality. As noted, some of the chapters deal very skillfully with topics in coercion as it is usually defined. Others are concerned with power relationships and not coercion. Coeditor Krause’s very carefully researched chapter presents a theory of “when and how . . . insurgencies and national movements succeed or fail” (p. 138). The theory describes how the structure of groups in a national movement and their relative power affects the movement’s likelihood of success. This is a theory about power, not coercion. Similarly, James Igoe Walsh’s chapter on drones (“Is Technology the Answer?”) takes it for granted that the U.S. drone campaign against the Islamic State (ISIS) is an attempt at coercion, but what it actually describes is a denial mission intended to degrade and destroy the organization. In “Prices or Power Politics?” Jonathan Markowitz presents an exciting theory about a state’s domestic structure and how it determines whether it will seek to actively control resources or pursue them through open markets. This is not, however, a theory explaining when and why a state chooses to employ threats to persuade another to change its behavior. Criticizing a work for its definition of key terms may seem pedantic, but in this case, the failure to clearly distinguish between coercion and brute force (or any other use of power in international politics) diminishes the volume’s contribution. For both scholars and practitioners, the failure to clearly identify what coercion is and is not makes it impossible to identify and measure the metrics by which we evaluate the success of actual policies.

Coercion presents several important new insights into behavior in the current international system. Greenhill and Krause’s volume sets itself a difficult challenge and ultimately stumbles over the scope of its own ambition. Progress in social science depends on the willingness to push beyond the boundaries of accepted wisdom, but only when grounded in the clear definition and application of analytical concepts.