This book began as a gnawing question: How can you deter two sides in a conflict? I thank John Ruggie for encouraging me, early on, to explore the obscure question in depth. My greatest intellectual debt is to Robert Jervis, who showed me why the question was not so obscure after all (indeed, that he had written a thing or two about it). Richard Betts also deserves credit, for what started me thinking about the question was his well-known argument in Foreign Affairs that it is often better to choose sides when intervening in conflicts. My thanks to Jervis and Betts for reading and critiquing my work; to Page Fortna, Kenneth Waltz, and Kimberly Zisk, who also gave valuable comments; and to Robert Art, Glenn Snyder, Mark Sheetz, and Keir Lieber, who all reviewed later versions of the manuscript and suggested improvements in content and form. I am also grateful to Roger Hay- don, Ange Romeo-Hall, and Cathi Reinfelder at Cornell University Press for expert guidance throughout the editorial process.
Others who deserve thanks for feedback on the project include Nora Bensahel, Chris Ball, Robin Bhatty, Mia Bloom, Derek Chollet, Tom Christensen, Stephen Cohen, Ivo Daalder, Sumit Ganguly, Bates Gill, Stacie Goddard, Talbot Imlay, Peter Jakobsen, Colin Kahl, Ron Krebs, Aaron Lobel, Jon Mercer, Dinshaw Mistry, Michael O'Hanlon, Robert Rauchhaus, Matthew Rendall, Evan Resnick, Jeff Ritter, Stephen Rosen, Robert Ross, Jordan Seng, Jeremy Shapiro, Jack Snyder, Marc Trachtenberg, Leslie Vinajamuri, Jon Western, Richard Wilcox, and Micah Zenko. I also owe a debt to many others who participated in seminars at Brookings Foreign Policy Studies, Columbia's Institute of War and Peace Studies, Harvard's Olin Institute of Strategic Studies, Yale's International Security Studies program, and the Boston College Department of Political Science.
Two research institutions provided crucial support for the bulk of my