Preventing Enemy Coalitions Preventing Enemy Timothy W. Crawford Coalitions How Wedge Strategies Shape Power Politics 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- 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 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/ISEC_a_00036 by guest on 01 October 2021 International Security 35:4 156 I deªne a “wedge strategy” as a state’s attempt to prevent, break up, or weaken a threatening or blocking alliance at an acceptable cost. When the strategy is successful, the state (i.e., the divider) gains advantage by reducing the number and strength of enemies organized against it. Because wedge strat- egies can turn opponents into neutrals or allies, they can trigger surprising power shifts with signiªcant consequences for war and peace and the trajec- tory of international politics. Adolf Hitler’s diplomatic coup of August 1939— the Nazi-Soviet nonaggression pact—dismantled the only counterbalancing coalition that could have derailed German aggression against Poland.3 On the other side of Eurasia, the Soviet Union secured Japanese neutrality in an April 1941 pact that held until August 1945, when the Soviet Union invaded Japanese-occupied Manchuria. The pact drove a wedge into the Axis alliance and was a boon to Soviet security after Germany’s invasion. In particular, Japan’s continued neutrality in late 1941 and early 1942 allowed massive trans- fers of Soviet military power from the Far East to the western front.4 Knowing tics, Vol. 61, No. 2 (April 2009), pp. 340–347; Norrin M. Ripsman and Jack S. Levy, “Wishful Thinking or Buying Time? The Logic of British Appeasement in the 1930s,” International Security, Vol. 33, No. 2 (Fall 2008), pp. 148–181; Daniel Byman and Matthew Waxman, The Dynamics of Coer- cion: American Foreign Policy and the Limits of Military Might (New York: Cambridge University Press, 2002), pp. 171–172; Stuart J. Kaufman, Richard Little, and William C. Wohlforth, eds., The Balance of Power in World History (Basingstoke, U.K.: Palgrave Macmillan, 2007); Schweller, Deadly Imbalances, pp. 77–78; Robert Jervis, System Effects: Complexity in Political and Social Life (Princeton, N.J.: Princeton University Press, 1997), pp. 188–191; Glenn H. Snyder, Alliance Politics (Ithaca, N.Y.: Cornell University Press, 1997), pp. 337–338; Richard Rosecrance and Chih-Cheng Lo, “Balancing, Stability, and War: The Mysterious Case of the Napoleonic International System,” International Studies Quarterly, Vol. 40, No. 4 (December 1996), pp. 479–500; Frederick H. Hartmann, The Rela- tions of Nations, 5th ed. (New York: Macmillan, 1978), pp. 333–337; George Liska, Nations in Alli- ance: The Limits of Interdependence (Baltimore, Md.: Johns Hopkins University Press, 1968), pp. 42– 60; and Ivo D. Duchacek, Conºict and Cooperation among Nations (New York: Holt Rinehart, 1960), pp. 372–377. See also Hans J. Morgenthau, Politics among Nations: The Struggle for Power and Peace (New York: Alfred A. Knopf, 1948), p. 134; George Modelski, A Theory of Foreign Policy (New York: Praeger, 1962), p. 132; A.F.K. Organski, World Politics, 2d ed. (New York: Alfred A. Knopf, 1968), pp. 278–279; and Waltz, Theory of International Politics, p. 118. For cross-disciplinary insights, see Eric A. Posner, Kathryn E. Spier, and Adrian Vermeule, “Divide and Conquer,” Olin Working Pa- per, No. 467 (Chicago: University of Chicago Law and Economics, May 26, 2009), http://ssrn.com/ abstractϭ1414319. 3. I discuss this case at length below. 4. See Boris Slavinsky, The Japanese-Soviet Neutrality Pact: A Diplomatic History, 1941–1945, trans. Geoffrey Jukes (New York: Routledge, 2004); and George A. Lensen, The Strange Neutrality: Soviet- Japanese Relations during the Second World War, 1941–1945 (Tallahassee: Diplomatic Press, 1974). “It is possible,” wrote Paul W. Schroeder, “that Russia was saved [in 1941] because Japan persisted in her refusal to launch an attack upon Siberia.” Schroeder, The Axis Alliance and Japanese-American Relations, 1941 (Ithaca, N.Y.: Cornell University Press, 1958), p. 166; see also p. 48. The Soviet redeployments from the Far East “played a vital role in the war in the west [and had] a signiªcant role in halting German forces on the approaches to Moscow and in launching the Red Army’s en- Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/ISEC_a_00036 by guest on 01 October 2021 Preventing Enemy Coalitions 157 more about when wedge strategies work and why can help scholars better ex- plain such intrinsically important historical contingencies as these. There are ªve other main reasons why it is useful to understand how wedge strategies work and when they are likely to succeed. First, leaders can use this information to craft policies designed to divide their adversaries or to defend their own states’ alliances. In particular, conceptual models of wedge strate- gies can help to frame options to divide potential adversaries in real-world scenarios. They can also highlight critical variables and favorable conditions, as well as the chances of success or failure.5 Second, understanding how and when wedge strategies work can illumi- nate a principal cause of war: states’ disagreements about relative power.6 A major source of such disagreements is differing expectations about who will ally with whom and who will decide to be neutral when conºict turns violent. Wedge strategies foster these kinds of disagreements and the uncertainties that underpin them. Third, knowing more about how wedge strategies work can strengthen scholars’ grasp of the substance of states’ external balancing behavior and thus contribute to more accurate theories of balancing.7 As substitutes to arms and alliance building, wedge strategies are among the options available to states seeking to balance against threats. A fuller understanding of wedge strategies can therefore help scholars better assess the presence of balancing behavior in speciªc cases, as well as the prevalence of balancing in international politics more broadly. Fourth, knowing how and when wedge strategies work can enable scholars suing counteroffensive.” David M. Glantz, The Soviet Strategic Offensive in Manchuria, 1945: “Au- gust Storm” (London: Frank Cass, 2003), pp. 5–6; for details of the transfers, see pp. 43–44 n. 11. 5. See Alexander L. George, Bridging the Gap: Theory and Practice in Foreign Policy (Washington, D.C.: United States Institute of Peace Press, 1993), chap.