At least since Thucydides, students of international relations have sought rational explanations for the advent of war. Rationalist explanations assume purposive action; states are said to make reasoned decisions about the use of force. Although rationalist explanations have proven persuasive, durable, and offer the basis for cumulative theorizing, they also imply substantial limits on what we can know about war. I show that the most general rationalist explanation for war also dictates that the onset of war is theoretically indeterminate. We cannot predict in individual cases whether states will go to war, because war is typically the consequence of variables that are unobservable ex ante, both to us as researchers and to the participants. Thinking probabilistically continues to offer the opportunity to assess international conflict empirically. However, the realization that uncertainty is necessary theoretically to motivate war is much different from recognizing that the empirical world contains a stochastic element. Accepting uncertainty as a necessary condition of war implies that all other variables—however detailed the explanation—serve to eliminate gradations of irrelevant alternatives. We can progressively refine our ability to distinguish states that may use force from those that are likely to remain at peace, but anticipating wars from a pool of states that appear willing to fight will remain problematic. For example, we may achieve considerable success in anticipating crises, but our ability to predict which crises will become wars will probably prove little better than the naive predictions of random chance. The need for uncertainty to account for war means that the same conditions thought to account for war must also exist among states not destined to fight. Otherwise, states themselves will differentiate between opponents in a way that either removes the motives for war or restores uncertainty. It has long been accepted that social processes possess an element of uncertainty, but the centrality of uncertainty to rationalist explanations for war means that the advent of war is itself stochastic. War is literally in the “error term.”

What motivates states to follow international norms, rules, and commitments? All social systems must confront what we might call the problem of social control—that is, how to get actors to comply with society's rules—but the problem is particularly acute for international relations, because the international social system does not possess an overarching center of political power to enforce rules. Yet, taken in balance with other values, a measure of order is a valued good. Some take this absence of centralized power to mean that the international system is like a Hobbesian state of nature, where only material power matters; others see it as evidence that international rules have force only when they are in the self-interest of each state. I show that these two conclusions are premature because of their shallow reading of international society and misinterpretation of the ways in which authority works in domestic society.

Andrew Moravcsik's article titled “A New Statecraft? Supranational Entrepreneurs and International Cooperation” is a powerfully argued and provocative contribution to our understanding of the role of individuals in the dynamics of international cooperation. His revisionist account of the parts played by prominent figures like Jean Monnet and Jacques Delors in the development of the European Union (EU) is sufficient all by itself to ensure that this piece will stimulate vigorous debate.

Gary King, Robert O. Keohane, and Sydney Verba's Designing Social Inquiry exploits the metaphor of researcher-as-statistician to develop guidelines for conducting social scientific research that are allegedly applicable to all empirical investigations. Their approach has sharp and often unflattering implications for case studies and similar research strategies. Because their statistical worldview is unable to make sense of important aspects of case study research or of the importance that is sometimes attached to the findings of a single case, their argument seemingly casts doubt on the wisdom of producing or consuming such studies.

I argue that the foundation of classical statistics and the epistemology of Carl Hempel and Karl Popper is an inadequate and misleading basis for a critical evaluation of case studies. I then present examples of research that are not easily accommodated within the authors' framework and sketch the elements of an alternative epistemological framework rooted in a “pattern” model of explanation. The latter is a standpoint that is much more helpful in understanding and criticizing case studies than the framework presented in Designing Social Inquiry.

Economic regionalism appears to be growing rapidly. Why this has occurred and what bearing it will have on the global economy are issues that have generated considerable interest and disagreement. Some observers fear that regional economic institutions—such as the European Union (EU), the North American Free Trade Agreement (NAFTA), Mercosur, and the organization of Asia-Pacific Economic Cooperation (APEC)—will erode the multilateral system that has guided economic relations since the end of World War II, promoting protectionism and conflict. Others argue that regional institutions will foster economic openness and bolster the multilateral system. This debate has stimulated a large and influential body of research by economists on regionalism's welfare implications.

Under what conditions do officials in international organizations wield influence as informal political entrepreneurs? Two conditions, I argue in the article under discussion, must obtain: First, an asymmetry in the availability of information or ideas must impede national governments from negotiating Pareto-efficiently. High transaction costs, relative to gains, must induce a coordination failure. Actors able to provide the three essential entrepreneurial functions—initiatives, mediation, mobilization—must be scarce. Second, international officials must enjoy or be accorded privileged access to the information or ideas necessary to act as entrepreneurs and induce more efficient interstate bargains. Where either of these two conditions is absent, third-party entrepreneurial activities are likely to be redundant (because states, as stakeholders, would have greater means and incentives to act as entrepreneurs) or futile (because a consensual support among states would not be forthcoming anyway).

Analysts of the European Union (EU) and international bargaining have generally failed to appreciate how the shift within the EU from unanimity to qualified majority voting has affected European bargaining positions and international outcomes. I analyze the international effects of changes in EU decision-making rules with a simple spatial model and assess the utility of the model in two cases of environmental bargaining that span the entry into force of the Maastricht Treaty. The EU can decisively shape international outcomes by concentrating the weight of its fifteen member states on a single substantive position and rendering that position critical to any internationally negotiated agreement. The findings generalize to numerous areas of EU external relations and suggest that analysts should attend specifically to the EU and more generally to domestic and regional institutional factors in explaining international bargaining outcomes.