Realists see systemic competition as the key to international politics and expect states to converge on something like “best practice” under this competitive pressure. For realists, this should be especially true for military practices, where the penalties for suboptimality are most severe. Realism thus predicts rapid and comprehensive diffusion of military methods, with all quickly emulating the state of the art as demonstrated by the strongest. This view is shared by policymakers who worry about technology transfer and its security implications: Can America preserve its current advantages in the use of networked information and precision weaponry as technology and ideas spread to potential challengers?

The authors in this anthology challenge both this realist expectation of convergence and the policy directions it implies. Diffusion, they find, is neither automatic nor universal. Instead, it is highly contingent, with a host of unit-level variables intervening to deflect many states from adopting the apparent military state of the art. Others pursue this state of the art, but they do so not from military competitive pressures but for reasons of prestige or conformance with transnational norms having no immediate military payoff. The result is greater variety in military practice than realists would predict, less connection between military practice and objective threats, and a larger role for unit-level and transnational variables in international politics. This in turn presents a mixed bag for policymakers. Diffusion may be slower or less complete than some fear. But many of the key determinants are nonmanipulable features of states and cultures. Hence, where diffusion can occur, there may be little that policymakers can do to steer or prevent it.

The results are persuasive and important. Many identify strategic studies with realism, assuming that concern with the conduct of war must exclude interest in culture, norms, or domestic politics. This volume shows that clear-eyed analysis of war may require systematic treatment of unit-level and ideational variables—the balance of material resources is not enough. Growing interest in unit-level, nonmaterial variables is among the most important trends in modern strategic studies; this volume reinforces this direction and adds much useful empirical detail.

The volume is also well crafted and the authors well chosen. The editors have clearly worked hard to keep the organization coherent and to structure the chapters around consistent crosscutting themes. The chapter authors are uniformly strong. The Geoffrey Herrerra-Thomas Mahnken chapter is particularly well done, but (unusual for an anthology) there are few real clinkers in a consistently strong collection here.

The volume is a model for policy-relevant scholarship. The authors speak to questions of central importance for international relations theory and strategic studies, but they frame their questions in terms that enable implications to be drawn for policy decision making. Sometimes these implications prescribe action (e.g., when attempting to transplant doctrines or concepts elsewhere, adapt them to local culture rather than simply imposing foreign ideas). Sometimes, however, the authors caution that effective action may not be possible: Where outcomes turn on nonmanipulable variables, the mark of wisdom may be to recognize one's limits rather than attempting the impossible.

Of course, there are ways the analysis could have been strengthened. The focus on diffusion, for example, could have been framed in a larger context. Diffusion, after all, is a subset of innovation (diffusion is innovation derived from abroad), which is, in turn, a subset of doctrine and strategy (innovation is doctrinal or strategic change). Both innovation and the determinants of doctrine per se have been extensively studied; diffusion is certainly an important special case of these broader phenomena, but if treated as a special case rather than an autonomous subject matter, it might have been possible to draw upon a wider theoretical literature and thereby to sharpen the theoretical insights derived.

The book also has the weaknesses of its strengths. As an anthology, it is well suited to the enumeration of a wide range of factors that might bear on diffusion and to the identification of the multiple causal paths through which this variety of variables might operate. But anthologies are typically better at enumerating than at culling, prioritizing, or integrating such variety into determinate, parsimonious theory, and this one is no different. Causal attribution, moreover, is sometimes assumed rather than demonstrated: Chapter authors more often show covariance of a unit-level attribute and a diffusion outcome than they establish that the outcome was due to the attribute.

Finally, one of the book's more interesting policy findings—that today's ongoing information revolution will inevitably spread, posing dangerous security implications (p. 402)—is in tension with many of the supporting chapters. Certainly, many states have competitive incentives to acquire information technology (IT) and adapt it to war making. And the commercial impetus for IT diffusion reduces cost barriers to military adaptation: Economic globalization makes cheap IT widely available regardless of military needs. Yet if successful diffusion turns on culture, domestic politics, or organization—as most of the book contends—then mere availability of cheap hardware does not imply corresponding military capability. Efficient military use of networked information could easily prove as culturally or politically or organizationally bound as efficient use of any of the other foreign innovations considered here. On the contrary, one could easily use the analyses here to challenge claims for a looming global military revolution based on the rapid spread of IT: In a realist world of rapid, uniform response to competitive incentive, diffusion would be likely; in a contingent, messy world of unit-level and cultural constraint, convergence faces daunting challenges.

Overall, though, The Diffusion of Military Technology and Ideas is an important contribution. Whatever one's views on convergence or the emerging military role of IT, this book will be essential for making—or breaking—one's case.