I thank Robert Art, Ajin Choi, Peter Feaver, and David Priess for their comments on this paper. I also received helpful comments when I delivered earlier drafts to a session of the Peter B. Lewis Series on "New Thinking in International Relations Theory," sponsored by the Center of International Studies, Princeton University, April 30, 1992, and to a panel at the "Workshop on International Relations Theory: At the Crossroads of the Post-Cold War Era," sponsored by the Institute of International Relations, Panteion University, Athens, May 27, 1994.