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Neo-realist Theory I Realism has been for some time the reigning tradition in international theory and remains a major current in it.’ The neo-realism or structural realism developed in Kenneth N. Waltz’s Theory of International Politics is generally considered a major advance on the classical version of Hans Morgenthau and others. The central argument is that the broad outcomes of international politics derive more from the structural constraints of the states system than from unit behavior. The theory proceeds in a series of logical inferences from the fundamental postulate of a states system in which all units are autonomous, so that the system is structured by anarchy rather than hierarchy; to the primacy of The author is a member of the Departments of History and Political Science at the University of Illinois, Urbana. Much of the research and writing of this article was done while the author was a Jennings Randolph Peace Fellow at the United States Institute of Peace; its support is here gratefully acknowledged. Helpful criticism and suggestions have been given by Robert Jervis, JackSnyder, Robert 0.Keohane, Patrick Morgan, Edward Kolodziej, Bruce Russett, Joseph Kruzel, Jennifer Mitzen, Michael Lund, Joseph Klaits, and the members of seminars at the U.S. Institute of Peace, Columbia University’s Institute for War and Peace Studies, and the University of Chicago ’s Program on International Politics, Economics, and Security. They are likewise gratefully acknowledged. 1. The central work is Kenneth N. Waltz, Theory ofznternational Politics (Reading, Mass.: AddisonWesley , 1979). Other expositions by Waltz of his position are his Man, the State, and War: a Theoretical Analysis (New York: Columbia University Press, 1959); ”The Origins of War in Neorealist Theory,” in Robert I. Rotberg and Theodore K. Rabb, eds., The Origin and Prevention of Major Wars (Cambridge: Cambridge University Press, 1989), pp. 39-52; and “The Stability of a Bipolar World,” Daedalus, Vol. 93, No. 3 (1964), pp. 881-909. Robert J. Art and Kenneth N. Waltz, eds., The Use of Force: Military Power and lnternational Politics, 4th ed. (Lanham, Md.: University Press of America, 1993) contains many articles exemplifying neo-realist arguments and assumptions, including three by Waltz. Other versions and applications of realist theory may be found in Stephen M. Walt, The Origins of Alliances (Ithaca, N.Y.: Cornell University Press, 1987);Barry R. Posen, The Sources of Military Doctrine: France, Britain, and Germany Between the World Wars (Ithaca, N.Y.: Cornell University Press, 1984); Robert Gilpin, War and Change in World Politics (Cambridge: Cambridge University Press, 1981);and John Mearsheimer, Conventional Deterrence (Ithaca, N.Y: Cornell University Press, 1983).For a good introduction to realism and its chief current rival, idealism, see Joseph S. Nye, Jr., Understanding lnternational Conflicts: An Zntroduction to Theory and History (London: HarperCollins, 1993).The classic work of the older realism, emphasizing the state‘s natural drive for power rather than structural constraints as the chief source of power politics and conflict, is Hans Morgenthau, Politics Among Nations: The Struggle for Power and Peace (New York: Knopf, 1948). International Security, Vol. 19, No. 1(Summer 1994), pp. 108-148 0 1994 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology 108 Historical Reality vs.Neo-realist Theory I 109 survival, security, and independence for each unit wishing to remain part of the system; to the mandate of self-help this need imposes upon each unit; and to a resultant competition between units which produces a recurrent pattern of various balances of power. (See Figure 1.) Much current debate over neo-realism centers on what implications the end of the Cold War might have for realist theory, in terms of its ability both to explain this particular outcome and to prescribe future policy.2This essay Figure 1. Neo-realism. States system 1 Structural anarchy .1 Primacy of security 1 1 Self-help Balance of power 2. For current neo-realist arguments, see John Mearsheimer, “Back to the Future: Instability in Europe After the Cold War,” International Security, Vol. 15, No. 1 (Summer 1990), pp. 5-55; Christopher Layne, ”The Unipolar Illusion: Why New Great Powers Will Rise,” International Security, Vol. 17, No. 4 (Spring 1993), pp. 5-51...