International trade is often wrapped up in a package with many good things—wealth, development, democracy, and peace. The proposition that increased trade is related to pacific international relations is one of the most well-known tenets of liberal theory. Despite its long history in political thought, the relationship between trade and peace has not been subject to extensive and systematic analysis until recently. In this edited volume, Edward D. Mansfield and Brian M. Pollins collect some of the most current thinking addressing the theoretical and methodological issues that arise in the quest to conceptualize and test the relationship between economic interdependence and international conflict. Understanding this relationship is important both theoretically and for policy reasons: Many policymakers today assume that increased trade will create a more peaceful world.

The introductory chapter by Mansfield and Pollins is worth the price of the book alone. They examine the evolution of research on this topic, surveying the different approaches and their strengths and weaknesses, and making valuable suggestions for future research. Anyone interested in becoming quickly familiar with the main lines of debate could do no better than to read this chapter closely. However, close reading of the rest of the volume is rewarding in demonstrating the wide range of approaches, criticisms, and empirical analyses of this topic. The volume as a whole is organized into two sections—the first addressing the theoretical foundations of the interdependence-conflict link, and the second examining methodological issues and developments.

A number of themes run throughout the 20 chapters. Many authors correctly point to the need to go beyond positing a correlation between economic interdependence and peace to examine the causal logic behind it. In other words, if the relationship holds, we need to understand why and how this might be so. This requires a theory of the state and its relationship to society (Beth Simmons); analysis of domestic politics, including the role of democracy, leadership, and domestic coalitions (Christopher Gelpi and Joseph M. Grieco, Etel Solingen, Gregory D. Hess); and economic statecraft (Bruce Russett, Michael Mastanduno).

The authors differ in the emphasis they place on whether trade influences the likelihood of conflict through economic opportunity costs, versus its role in signaling intentions and providing information. The classic liberal argument of Kant is that war is too costly when trade between countries is high. James D. Morrow, Erik Gartzke, and Arthur A. Stein argue instead that trade provides information that signals intentions. Jack Levy's chapter explores more fully the economic opportunity cost hypothesis, but includes issues of strategy, credibility, and information in an extensive examination of alternative explanations. Russett and Mastanduno treat trade as an instrument of policy, without adopting the information/signaling approach. Russett argues that trade suppresses violent conflict, in combination with other factors such as democracy and alliances. Mastanduno is skeptical about the long-term effectiveness of using trade to change the foreign policy of another state. Both Russett and Levy, in very different ways, address research design issues that come up again in the chapters devoted specifically to methodology.

The authors demonstrate effectively that different definitions of the two key variables of interdependence and conflict can lead to different results. Kant's original argument was that trade reduces war, but recent research has often used data on militarized interstate disputes (MIDs) instead. Other definitions of the dependent variable are possible, such as political contests (Gartzke); trade conflict (Stein); regional stability (Solingen); or some combination of war, MIDs, and fatal disputes (Russett). Interdependence is most often defined in terms of the trade/GDP ratio, which both Russett and John Oneal defend. But it might also be conceptualized to include capital flows or globalization (Gartzke, Norrin M. Ripsman, and Jean-Marc F. Blanchard) or preferential trading arrangements (Edward D. Mansfield). One of the key areas of methodological debate is whether the unit of study is the state, or dyads, and results vary significantly depending on the approach adopted.

Most of the authors here are sensitive to issues of research design and methodology. Levy summarizes a broach range of alternative explanations for the trade-peace proposition, and assesses the appropriate use of large-n research and case studies. While recent advances in this research program have come from large-n data analysis, the volume concludes with two interesting chapters that examine the value of qualitative approaches (Ripsman and Blanchard) and simulations (David H. Bearce and Eric Fisher). Both Katherine Barbieri and Jon C. Reuveny provide excellent overviews of the biases and constraints in the data, such as the lack of complete historical data, limited information on the developing world, and the fact that most existing data is annual and not continuous. A number of authors point to time as an important confounding variable, with Janet Box-Steffensmeier, Dan Reiter, and Christopher J. Zorn surveying new statistical models that incorporate the temporal dimension. Richard Timpone, in a fairly technical chapter, discusses statistical techniques to take account of the endogeneity of the two main variables.

A number of the authors included here are not typically associated with the interdependence-conflict research program, but they consider this program in light of their own theoretical and empirical work. This widens the application of their own research and demonstrates the relevance of this program to broader questions in international relations. The trade-off made in putting together this comprehensive collection of authors is that chapters are necessarily short, leaving one wanting to see more. Many of the pieces simply introduce an issue or problem without carrying through with an application.

Not all of the chapters work as well as others, and not all the arguments are clearly presented or persuasive. The authors themselves certainly do not all agree on the issues they raise, but they engage the reader in an ongoing set of debates. It is interesting that both Simmons and Barbieri are alone in including Marxist theories as part of their discussion. Simmons takes seriously Marxist theories of the state, and Barbieri looks at dependence as a characteristic of trade relations. Only one author, Mastanduno, brings in a policy dimension, and yet it would have been interesting to include a chapter devoted to the way in which the trade-peace link has been adopted into actual policy. Despite the flaws inevitable in a volume of this scope, this is an excellent survey of the theoretical and methodological issues that animate the interdependence-conflict debate. Economic Interdependence and International Conflict should be valuable to anyone who seeks to understand the accumulation and development of research in international relations.