How do states dis- suade adversaries from organizing against them? When do they succeed in splitting opponents that have formed or are likely to form an alliance? How do such “wedge strategies” inºuence larger patterns of international politics? Scholars have focused much attention on how alliances form and whether they are driven by balancing, bandwagoning, or other dynamics. 1 They have paid less attention to the role of wedge strategies in disrupting or preventing the formation of alliances and to understanding how and when those strategies succeed. 2 Timothy W. Crawford is Associate Professor of Political Science at Boston College. For helpful comments and discussion on earlier drafts, the author would like to thank Jonathan Caverley, Michael Glosny, Stacie Goddard, Yasuhiro Izumikawa, Ronald Krebs, Orly Mishan, T.V. Paul, Evan Resnick, Norrin Ripsman, Robert Ross, Jack Snyder, Karen Yarhi-Milo, and the anony- mous reviewers. He would also like to thank participants in conference panels at meetings of the American Political Science Association and International Studies Association, as well as seminar participants at Harvard University’s John M. Olin Institute for Strategic Studies and the Massa- chusetts Institute of Technology’s Security Studies Program, for their comments and suggestions. The following Boston College undergraduate and graduate research assistants also deserve thanks: Raakhi Agrawal, Danielle Cardona, Jonathan Culp, Alexandre Provencher-Gravel, and Amanda Rothschild. 1. Kenneth N. Waltz, Theory of International Politics (New York: Random House, 1979); Stephen M. Walt, The Origins of Alliances (Ithaca, N.Y.: Cornell University Press, 1987); Paul Schroeder, “Histor- ical Reality versus Neo-realist Theory,” International Security, Vol. 19, No. 1 (Summer 1994), pp. 108–148; Thomas J. Christensen and Jack Snyder, “Chain Gangs and Passed Bucks: Predicting Alliance Patterns in Multipolarity,” International Organization, Vol. 44, No. 2 (Spring 1990), pp. 137– 168; Randall L. Schweller, Deadly Imbalances: Tripolarity and Hitler’s Strategy of World Conquest (New York: Columbia University Press, 1998); John J. Mearsheimer, The Tragedy of Great Power Politics (New York: W.W. Norton, 2001); John A. Vasquez and Colin Elman, eds., Realism and the Balancing of Power: A New Debate (Upper Saddle River, N.J.: Prentice Hall, 2003); and T.V. Paul, James J. Wirtz, and Michel Fortmann, eds., Balance of Power: Theory and Practice in the 21st Century (Palo Alto, Ca- lif.: Stanford University Press, 2004). 2. For an initial effort by this author, see Timothy W. Crawford, “Wedge Strategy, Balancing, and the Deviant Case of Spain, 1940–41,” Security Studies, Vol. 17, No. 1 (Winter 2008), pp. 1–38. Other important recent studies include Yasuhiro Izumikawa, “United We Stand, Divided They Fall: Use of Coercion and Rewards as Alliance Balancing Strategy,” Ph.D. dissertation, Georgetown Univer- sity, 2002; Victoria Tin-bor Hui, War and State Formation in Ancient China and Early Modern Europe (Cambridge: Cambridge University Press, 2005); Stacie E. Goddard, “When Right Makes Might: How Prussia Overturned the European Balance of Power,” International Security, Vol. 33, No. 3 (Winter 2008/09), pp. 110–142; Daniel H. Nexon, The Struggle for Power in Early Modern Europe: Re- ligious Conºict, Dynastic Empires, and International Change (Princeton, N.J.: Princeton University Press, 2009); and Michael Glosny, “The Grand Strategies of Rising Powers: Reassurance, Coercion, and Balancing Responses,” Ph.D. dissertation, Massachusetts Institute of Technology, 2011. Key discussions are also found in Daniel H. Nexon, “The Balance of Power in the Balance,” World Poli- Preventing Enemy Coalitions Preventing Enemy Coalitions Timothy W. Crawford How Wedge Strategies Shape Power Politics International Security, Vol. 35, No. 4 (Spring 2011), pp. 155–189 © 2011 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology. 155