When faced with separatist movements, why do states choose violence over accommodation? War, after all, is an exceedingly costly outcome, one that any rational decision maker should eagerly avoid. Yet, more often than not, states reject separatist demands, and opt instead to fight bloody civil wars.

Why states choose war over accommodation is the puzzle that drives Barbara Walter's excellent book, her second major project on the causes of civil war. Most scholars suggest that states fight because they value territory, which “often contains important natural resources, serves a vital security function, or plays a critical role in the identity of a country” (p. 5). But Walter contends that while these existing accounts are intuitive, they are insufficient—they fail to explain why states pay such an awful price for what is ultimately a negotiable good.

Key to solving this puzzle, the author argues, is reputation. States fight not because territory has any particular value but “because fighting helps them deter other groups from seeking secession in the future” (p. 7). State leaders must worry not only about the stakes in the present negotiations but also about the costs of future claims. And while accommodation might prevent war, it also serves as a signal to other minorities that the state is weak, prompting additional challenges too costly for a state to bear. To preserve a reputation for toughness and deter further deterioration of the state, leaders will thus refuse to yield to separatist demands.

Reputation is a concept that has fallen out of favor in international relations, with scholars arguing that there is little evidence to suggest that reputations actually affect state behavior (e.g., see John Mercer, Reputation and International Politics, 1996). Walter tackles these criticisms head-on, suggesting that researchers ask not whether reputations matter but under what conditions states will seek to protect their image. She parses through these conditions in a theory chapter that meticulously details when and why state leaders care enough about their reputation to resort to violence. First and foremost among these conditions, she argues, is the number of possible separatist groups within the state itself. As she argues, “a government's decision to accommodate a group seeking self-determination will be inversely related to the number of ethnic groups in that country” (p. 25). The more potential challengers, the more a government must preserve a reputation for toughness, lest it invite further challenges to its sovereignty.

Walter also elucidates the conditions under which separatist groups are likely to challenge the state. Separatists, after all, should recognize that governments care about their reputations, which means that there will be more or less ideal times to demand territory (indeed, one thing that really differentiates Walter's book from other studies of ethnic conflict is her insistence that both governments and separatists are rational actors—separatist groups are not irrational but are equal partners in strategic interaction). She argues that separatists will wait until reputational costs are low to pursue their case. When there are few other challengers, for example, or when a leader's tenure is almost up, a state's concerns about reputation should diminish, and minorities should expect more success when pressing their claims.

The bulk of the book tests these hypotheses with three different methods. The first of these is an experimental study. Working with chapter coauthor Dustin Tingley, Walter uses laboratory experiments to test whether individuals—in this case, Princeton undergraduates—protect their reputations in the way her model predicts. In the experiment, individuals clearly valued their reputations; in fact, they defended their reputations beyond what the model would suggest. But while these experiments allowed Walter to clarify and adjust her theory, it is unclear whether they are a good test of her hypotheses. Whether readers believe experiments are useful, I suspect, will depend on how they perceive the contributions of behavioral economics to international relations. For my part, I had a hard time getting beyond the fact that states—for better or worse—are not Princeton undergraduates, and that individual psyches operate somewhat differently than do collective governments.

More convincing were the two chapters of quantitative data analysis, the first of which tests hypotheses about reputation and state behavior, and the second, hypotheses about separatist groups. Walter's data collection is impressive, and her discussion of coding and of her models is clear and accessible to a broad audience. In these chapters, she finds significant support for her hypotheses. Governments, for example, are less likely to accommodate separatists when faced with several potential challengers, and separatists are less likely to pursue self-determination under these conditions. Moreover, these chapters suggest that conventional explanations are wanting—neither economic nor symbolic value determines a state's decision to fight (the author rightly points out, however, that measures of symbolic value are tricky, and better measures might produce different results).

Such large-n case studies say little about causality, however, as Walter herself notes (p. 133). Reputation provides one logical connection between the number of challengers and violence, but so might other explanations (the dynamics of postcolonial states comes to mind). This is why case studies are so critical—scholars can use cases to trace causal mechanisms and to examine if reputation was actually at the root of government and separatist decision making. Here, Walter tests her theory in two cases, looking at separatist movements in Indonesia and the Philippines. In Indonesia, where there are several potential separatist groups, the government cracked down on self-determination movements in places like East Timor and Aceh. She makes a persuasive case that reputation drove Indonesia's leaders to violence, showing that government elites went to great lengths to publicize their brutality, signaling to others that demands for self-determination would not be treated kindly. In contrast, in the Philippines, a state with few ethnic minorities, reputation was less important. As a result, groups frequently demanded autonomy, and all received concessions as a result (although, as Walter admits, not as quickly as her model would predict).

The author's case studies certainly demonstrate that reputations matter in government and separatist decisions. But her work also hints at theoretical avenues left unexplored. Domestic politics, for example, played a critical role in both cases. In the Philippines, the government resisted Muslim demands not only because of reputation but also because the government feared that concessions would anger its Christian support base. Perhaps more significantly, the case studies demonstrate that reputation is a more complex and malleable phenomenon than Walter's theory allows. In her spare model, stable structural factors, such as the number of minorities or the length of a leader's tenure, determine the importance of reputation. The case studies, in contrast, suggest that leaders have the power to shape their reputations beyond what structural factors should allow. In Indonesia, for example, leaders successfully defined East Timor as different form other separatist movements—the government's accommodation here, thus, could not be applied to other groups.

What this suggests is that Walter's work should be taken as a good first step but not the last word on the subject of reputations in civil war, or in international relations as a whole. Instead, scholars would do well to build on Walter's theory, exploring how leaders build and lose reputations, and how this process affects the prospects of war and peace.