When a statistical equation incorporates a multiplicative term in an attempt to model interaction effects, the statistical significance of the lower-order coefficients is largely useless for the typical purposes of hypothesis testing. This fact remains largely unappreciated in political science, however. This brief article explains this point, provides examples, and offers some suggestions for more meaningful interpretation.I am grateful to Tim McDaniel, Anne Sartori, and Beth Simmons for comments on a previous draft.

Why do some wars result in the intentional killing of large numbers of civilians? In this article we examine the incidence of mass killing in all wars from 1945 to 2000. In the statistical analysis of our data set of 147 wars, we find strong evidence supporting our hypothesis that mass killing is often a calculated military strategy used by regimes attempting to defeat major guerrilla insurgencies. Unlike conventional military forces, guerrilla armies often rely directly on the local civilian population for logistical support. Because guerrilla forces are difficult to defeat directly, governments facing major guerrilla insurgencies have strong incentives to target the guerrillas' civilian base of support. We find that mass killing is significantly more likely during guerrilla wars than during other kinds of wars. In addition, we find that the likelihood of mass killing among guerrilla conflicts is greatly increased when the guerrillas receive high levels of active support from the local population or when the insurgency poses a major military threat to the regime.For their helpful comments on previous versions of this article the authors thank Bear Braumoeller, Alex Downes, Jim Fearon, Hazem Goborah, Stathis Kalyvas, Gary King, Will Lowe, Matthew Krain, Lisa Martin, Manus Midlarsky, Bruce Russett, Nicholas Sambanis, Naunihal Singh, Abdulkader Sinno, Allan Stam, Jeremy Weinstein, and the anonymous reviewers of International Organization. We are also grateful to Wolfgang Moehler for his research assistance.Our coauthor Dylan Balch-Lindsay was killed in an automobile accident on 1 September 2002, cutting short a promising career. He was a gifted young scholar, without whom this article would not have been possible. He is sorely missed by his friends and colleagues. Donations in his name can be sent to the Dylan Balch-Lindsay Memorial Fund for Graduate Education/Foundation of the University of New Mexico, c/o Carol Brown, Department of Political Science, University of New Mexico, Albuquerque, NM, 87131-1121.

Some member-states of the European Union (EU) want a supranational foreign and security policy, while other member-states oppose any significant limitation of national sovereignty in this domain. What explains this variation? Answering this question could help us to better understand not only the trajectory of European unification, but also the conditions and prospects of consensual political integration in other regional contexts and territorial scales. The main research traditions in international relations theory suggest different explanations. I examine the roles of relative power capabilities, foreign policy interests, Europeanized identities, and domestic multilevel governance in determining the preferences of the fifteen EU member governments concerning the institutional depth of their foreign and security policy cooperation. I find that power capabilities and collective identities have a significant influence, but the effect of ideas about the nature and locus of sovereignty, as reflected in the domestic constitution of each country, is particularly remarkable.A previous version of this article was presented at the 4th ECPR Pan-European International Relations Conference, Canterbury, 8–10 September 2001. For their valuable comments, I would like to thank Filippo Andreatta, Daniele Archibugi, Simone Borra, Nicola Dunbar, Fabio Franchino, Alkuin Kölliker, Leonardo Morlino, Angelo Panebianco, Eiko Thielemann, Ben Tonra, the editors of IO, and three anonymous reviewers. I am responsible for any mistakes.

How can one explain cross-national differences in innovative activity across the industrialized democracies? In this article, I examine the “varieties of capitalism” (VOC) response to this question. VOC theory predicts that societies with liberal-market economies will direct their inventive activity toward radical technological change, while societies with coordinated-market economies will direct their inventive activity toward incremental technological change. I find that these predictions are not supported by the empirical data, and that the evidence offered by VOC proponents depends heavily on the inclusion of a major outlier, the United States, in the class of liberal-market economies. My empirical investigation includes simple patent counts, patents weighted by forward citations, and scholarly publications (both simple counts and citations-weighted). I analyze data covering all of the VOC countries over the course of several decades, little of which reveals the innovative patterns predicted by VOC scholars.For their excellent insights, critiques, and encouragement I gratefully thank Thomas Cusack, Tracy Gabridge, Michael Brewster Hawes, Derek Hill, Daniel K. Johnson, Chappel Lawson, Mark Lewis, Benedicta Marzinotto, Andrew Miller, Michael Piore, Jonathan Rodden, Herman Schwartz, James Snyder, David Soskice, Edward Steinfeld, Scott Stern, Dan Winship, the editors at International Organization, and two anonymous reviewers.

The effect of foreign aid on regime type in recipient countries remains widely debated. In this research note, I argue that a recent focus on “moral hazard” has distracted attention from another mechanism linking foreign aid to domestic political institutions. During the Cold War, donors' geopolitical objectives diminished the credibility of threats to condition aid on the adoption of democratic reforms. The demise of the Soviet Union and the end of the Cold War, on the other hand, enhanced the effectiveness of Western aid conditionality. I reanalyze an important recent study and demonstrate that the small positive effect of foreign aid on democracy in sub-Saharan African countries between 1975 and 1997 is limited to the post–Cold War period. This new empirical evidence underscores the importance of geopolitical context in conditioning the causal impact of development assistance, and the evidence confirms that the end of the Cold War marked a watershed in the politics of foreign aid in Africa.I would like to thank Henry Brady, Jennifer Bussell, Ruth Berins Collier, David Collier, Robert Powell, Jason Seawright, Beth Simmons, Laura Stoker, and two anonymous reviewers for their comments. I am also grateful to Arthur Goldsmith for sharing his data. Any errors are my own.

This article examines why international relations theories presume checks and balances but universal domination triumphed in ancient China. I argue that one should not presume the European experience as the norm and treat ancient China as a deviant case. I propose a dynamic theory of international politics that views international competition as processes of strategic interaction and that allows for alternative trajectories and endogenous transformation. Realist theories of international politics tend to focus on structural mechanisms and overlook agential strategies. At the same time, these theories focus on causal mechanisms that check attempts at domination and overlook mechanisms that facilitate domination. It is true that attempts at domination are checked by the mechanisms of balance of power and rising costs of expansion. But domination-seekers may overcome such obstacles by pursuing divide-and-conquer strategies, ruthless tactics, and self-strengthening reforms. From this strategic-interactive perspective, universal domination is no less possible than the balance of power.I would like to express my gratitude to Jack Snyder, Ira Katznelson, Charles Tilly, Thomas Bernstein, Michael Davis, and David Kang for their extensive comments on multiple drafts. I also want to thank Fiona Adamson, Bear Braumoeller, E. Bruce Brooks, Lars-Erik Cederman, Thomas Christensen, Claudio Cioffi-Revilla, Charles Cogan, Timothy Crawford, Julian Franklin, Taylor Fravel, Robert Goodin, Yoav Gortzak, A. Iain Johnston, Edward Kolodziej, Andrew Kydd, Mark Lewis, Daniel Nexon, Richard Rosecrance, Stephen Rosen, Peter Rutland, Mark Sheetz, Erik Voeten, R. Harrison Wagner, R. Bin Wong, and the editor-in-chief and two anonymous reviewers of International Organization for their thoughtful and critical comments. In addition, the Harry Frank Guggenheim Foundation, the Institute for the Study of World Politics, the Olin Institute for Strategic Studies at Harvard University, and the Center for International Security and Cooperation at Stanford University sponsored various phases of this project.