It is widely accepted that democracies are less conflict prone, if only with other democracies. Debate persists, however, about the causes underlying liberal peace. This article offers a contrarian account based on liberal political economy. Economic development, free markets, and similar interstate interests all anticipate a lessening of militarized disputes or wars. This “capitalist peace” also accounts for the effect commonly attributed to regime type in standard statistical tests of the democratic peace.

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Research appears to substantiate the liberal conviction that trade fosters global peace. Still, existing understanding of linkages between conflict and international economics is limited in at least two ways. First, cross-border economic relationships are far broader than just trade. Global capital markets dwarf the exchange of goods and services, and states engage in varying degrees of monetary policy coordination. Second, the manner in which economics is said to inhibit conflict behavior is implausible in light of new analytical insights about the causes of war. We discuss, and then demonstrate formally, how interdependence can influence states' recourse to military violence. The risk of disrupting economic linkages—particularly access to capital—may occasionally deter minor contests between interdependent states, but such opportunity costs will typically fail to preclude militarized disputes. Instead, interdependence offers nonmilitarized avenues for communicating resolve through costly signaling. Our quantitative results show that capital interdependence contributes to peace independent of the effects of trade, democracy, interest, and other variables.

Nuclear weapons proliferation is a topic of intense interest and concern among both academics and policy makers. Diverse opinions exist about the determinants of proliferation and the policy options to alter proliferation incentives. We evaluate a variety of explanations in two stages of nuclear proliferation, the presence of nuclear weapons production programs and the actual possession of nuclear weapons. We examine proliferation quantitatively, using data collected by the authors on national latent nuclear weapons production capability and several other variables, while controlling for the conditionality of nuclear weapons possession based on the presence of a nuclear weapons program. We find that security concerns and technological capabilities are important determinants of whether states form nuclear weapons programs, while security concerns, economic capabilities, and domestic politics help to explain the possession of nuclear weapons. Signatories to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) are less likely to initiate nuclear weapons programs, but the NPT has not deterred proliferation at the system level.

A basic debate in world politics involves the impact of intergovernmental organizations (IGOs) on international conflict. Liberals, functionalists, and others see IGOs as capable of transforming global anarchy, while realists emphasize the essential irrelevance of IGOs in managing such fundamental processes as war and peace. Recent quantitative studies also yield disparate conclusions depending on particular econometric assumptions, implying variously that IGOs foster pacific relations among states, have no impact on dispute behavior, or even increase dispute propensity. At least part of the problem is a lack of theoretical and empirical specificity. The authors apply bargaining theory to develop a “middle path” between the realist and liberal perspectives. Only some IGOs, those with security mandates and the most sophisticated institutional structures, are likely to influence dispute behavior. The authors combine the theory with two improvements in research design. First, IGOs vary in capability, mandate, and cohesion. The authors construct a dataset of IGO institutional heterogeneity and member cohesiveness. Second, states join IGOs for reasons that are not unrelated to why states fight. The authors control for the level of international involvement among countries and find support for their arguments in initial tests.

A debate exists over whether~and to what degree! the democratic peace is explained by joint democracy or by a lack of motives for conflict between states that happen to be democratic. Gartzke~1998! applies expected utility theory to the democratic peace and shows that an index of states' preference similarity based on United Nations General Assembly roll-call votes~affinity! accounts for much of the lack of militarized interstate disputes~MIDs! between democracies. Oneal and Russett 1997b, 1998! respond by arguing that UN voting is itself a function of regime type-that democracy "causes" affinity. Oneal and Russett seek to demonstrate their thesis by regressing affinity on democracy and other variables from a standard model of the democratic peace. I replicate results reported by Oneal and Russett and then extend the analysis in several ways. I find that the residuals from Oneal and Russett's regression of affinity remain highly significant as a predictor of the absence of MIDs. Further, significance for democracy is shown to be fragile and subject to variable construction, model specification, and the choice of estimation procedure.A fundamental positive goal of international relations is the explication of costly contests-students of world politics seek to understand why states fight. A fundamental normative goal of international relations is of course the alleviation of such contests. The democratic peace-the observation that liberal dyads seldom engage in militarized disputes-is exciting precisely because it offers important opportunities for addressing both of these goals. Still, unification of the two goals remains contingent on the character of the explanation. Any account that fits the facts is potentially useful in positive terms, but to fulfill the normative objective, accounts must offer causal variables either that are socially manipulable or that trend in a desirable direction. If the causes of the democratic peace lie in liberal politics or economics, then the foreign policies of leading powers or the inexorable march of time may yield an expanding sphere of pacific relations. If instead the democratic peace is substantially explained by variables that are unresponsive to autonomous policy efforts or that are more likely to wander than to trend, then the prospects for long-term peace remain in greater doubt.Here, I revisit a claim that the democratic peace can be explained largely as the product of similar interests. Quantitative studies of the democratic peace have been careful to control for the effect of realist variables~relative power, distance, etc.!, but they have largely ignored the impact of interest on international political behavior. If one believes that states are guided, not just by what

While most quantitative studies find a negative relationship between economic interdependence and interstate disputes, research by Barbieri finds that interdependence precipitates conflict. Participants in the debate suggest several causes, but we show that alternative variable constructions are sufficient to account for the discrepant findings. A simple formal equivalence unites respective operationalizations of dyadic interdependence used by Oneal & Russett (trade dependence, trade ij /GDP i ) and Barbieri (trade share, trade i /trade i ) with the consensus construction of monadic trade openness (trade i /GDP i ). We also show that Barbieri's trade share is negatively correlated with openness. Arguments in the article are verified through large-sample quantitative regression analyses of the two competing dyadic variable constructions and trade openness on MID onset. The results of these dyadic regression analyses show that trade share increases the probability of MID onset, trade dependence decreases the probability of MID onset and, correspondingly, that trade openness is negatively correlated with MID onset. * Equal authorship implied. We thank Han Dorussen, John Oneal, Bruce Russett, and several anonymous referees for comments and suggestions on earlier versions of this article. We also thank John Oneal and Katherine Barbieri for help with data. Alex Braithwaite provided valuable research assistance. The authors can be contacted by e-mail at: gartzke@columbia.edu and quanli@psu.edu. Data employed in this article can be obtained at http://www. prio.no/jpr/datasets.asp. Statistical analysis is conducted using Stata7.

A recent Climatic Change review article reports a remarkable convergence of scientific evidence for a link between climatic events and violent intergroup conflict, thus departing markedly from other contemporary assessments of the empirical literature. This commentary revisits the review in order to understand the discrepancy. We believe the origins of the disagreement can be traced back to the review article's underlying quantitative meta-analysis,