Grasping the Technological Peace: The Offense-Defense Balance and International Security

International Security, Vol. 25, No. 1 (Summer 2000), pp. 71–104© 2000 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology. 71 Grasping the Technological Peace Keir A. Lieber The Offense-Defense Balance and International Security Offense-defense theory argues that international conºict and war are more likely when offensive military operations have the advantage over defensive operations, whereas cooperation and peace are more likely when defense has the advantage. According to the theory, the relative ease of attack and defense—the offensedefense balance—is determined primarily by the prevailing state of technology at any given time. When technological change shifts the balance toward offense , attackers are more likely to win quick and decisive victories. This prospect of quick and decisive warfare exacerbates the security dilemma among states, intensiªes arms races, and makes wars of expansion, prevention, and preemption more likely. When technological innovation strengthens the defense relative to the offense, states are more likely to feel secure and act benignly.1 Offense-defense theory has deep roots, but has become increasingly popular in international relations scholarship and foreign policy analysis in recent years. The idea that the nature of technology affects the prospects for war and Keir A. Lieber is a Research Fellow in the Foreign Policy Studies Program at the Brookings Institution and a doctoral candidate in the Department of Political Science at the University of Chicago. For helpful comments and discussions, I thank Stephen Biddle, Meredith Bowers, Jasen Castillo, Alexander Downes, David Edelstein, Benjamin Frankel, Charles Glaser, Robert Lieber, John Mearsheimer , Robert Pape, Jordan Seng, Stephen Walt, Paul Yingling, two anonymous reviewers, and participants in the Program on International Politics, Economics, and Security at the University of Chicago. I would also like to thank the John D. and Catherine T. MacArthur Foundation, the Andrew Mellon Foundation, and the Smith Richardson Foundation for their generous support of this research. 1. The foundational works on offense-defense theory are Robert Jervis, “Cooperation under the Security Dilemma,” World Politics, Vol. 30, No. 2 (January 1978), pp. 167–214; George H. Quester, Offense and Defense in the International System (New York: John Wiley and Sons, 1977); and Stephen Van Evera, Causes of War: Power and the Roots of Conºict (Ithaca, N.Y.: Cornell University Press, 1999), especially chap. 6. For crucial theoretical developments, reªnements, and extensions, see Stephen Van Evera, “Offense, Defense, and the Causes of War,” International Security, Vol. 22, No. 4 (Spring 1998), pp. 5–43; Charles L. Glaser and Chaim Kaufmann, “What Is the Offense-Defense Balance and Can We Measure It?” International Security, Vol. 22, No. 4 (Spring 1998), pp. 44–82; Sean M. Lynn-Jones, “Offense-Defense Theory and Its Critics,” Security Studies, Vol. 4, No. 4 (Summer 1995), pp. 660–691; and Charles L. Glaser, “Realists As Optimists: Cooperation As SelfHelp ,” International Security, Vol. 19, No. 3 (Winter 1994/95), pp. 50–90. peace is simple, powerful, and intuitively plausible. Thus the offense-defense balance concept has been used to address a variety of important historical, theoretical, and policy questions even when scholars have not adopted the basic assumptions and logic of the theory.2 Perhaps the most important reason offense-defense theory continues to appeal to scholars is that it offers a compelling argument for why intense security competition among states is not an inevitable consequence of the structure of the international system. Speciªcally, for realists who believe that threats are more important than raw material power in explaining state behavior, the offense-defense balance appears to provide a systematic method of predicting when the balance of power is threatening and when it is not.3 Offense-defense ideas also continue to shape contemporary foreign policy debates on arms control, conventional and nuclear deterrence and force posture , the prevention of civil and ethnic conºict, and the so-called revolution in military affairs. On the latter issue, for example, the Economist recently proclaimed that the world is in the early stages of a new military revolution that will strengthen the offense relative to the defense and thus create “a strong incentive to strike ªrst.”4 The most policy-relevant conclusion offered by offense -defense...