Strange Bedfellows: The Strategic Dynamics of Major Power Military Interventions

Intuition suggests that major powers should be more likely to pursue joint military intervention when their preferences are most similar, but empirically, joint interventions are least likely in these cases. The solution to this puzzle lies in the strategic interaction between interveners. When states agree over policy, they face a free rider problem. A state is more willing to join an intervention as its preferences with the initial intervener diverge because doing so allows it to affect policy outcomes. To test the theory, a statistical model derived from the theoretical model is used to estimate the factors that affect the decisions of major powers to intervene in civil conflicts. Despite the existence of a norm of nonintervention in modern international law, major powers often intervene to affect the domestic policies and authority structures of less powerful states. However, the propensity of states to intervene varies. In 2003, the United States and some of its allies were willing to intervene militarily to install a more preferred regime in Iraq despite cries by many that such an action was illegitimate. At the same time, the major powers found themselves unwilling to intervene to end the genocide in Darfur, even though such an action may save thousands of lives and would be considered legitimate under international law. These recent examples highlight that intervention decisions, rather than being based largely upon legal or moral principles, are largely political in nature. The Iraq and Darfur examples also point to the fact that the propensity of major powers to pursue joint intervention is not necessarily related to the similarity of their preferences over the issues at stake. Despite some differences of opinion, the United States and Britain were willing to form a coalition to intervene in Iraq. On the other hand, while a majority of the countries in the world have signed the genocide convention, the major powers are unwilling to intervene jointly to stop the genocide in Darfur. Since states generally agree on many humanitarian issues, one might expect that major powers would be likely to pursue joint intervention in response to a humanitarian crisis, like genocide. Given the international consensus on the immorality of genocide and the high costs of intervention in such cases, major powers would be better off if they could act together and share the costs of ending a genocide. As Power (2002, 263) argues, “Genocide prevention is an immense burden that must be shared.” However, as the Rwanda genocide illustrated, the world community has generally failed to intervene and end mass killing (Valentino 2003). This disjuncture between the desire of states to end humanitarian crises and their actual behavior can be explained once one considers the strategic environment in which major powers interact. The analysis that follows shows that states are less willing to intervene jointly when they have similar preferences over the issues at stake. The reason behind this finding is intuitive. If states agree on an issue, they have incentives to free ride and let other states bear the costs of intervention. Joint intervention should be unlikely in cases where there is complete consensus on the issue at stake. Instead, states will be willing to intervene jointly when they disagree on some aspect of the issue. This divisive dimension provides a selective incentive that allows states to overcome the free rider problem. By intervening jointly, states gain benefits that they would not receive if they stayed out. To examine the strategic factors that lead major powers to intervene, as well as join or counter the interventions of others, I model the decision of two major powers to intervene in a third target state. The theory indicates that a major power is more likely to join or counter an intervention the farther its preferences are from the intervening power. To test the theory, a strategic choice statistical model derived from the theoretical model is used to estimate the factors that affected the decisions of major powers to intervene in countries undergoing civil conflicts from 1944 to 1998. The results provide strong support for the theory, indicating the utility of using game theory to examine the intervention decisions of states. The implications of the theoretical and statistical analysis also help to explain the intervention behavior of major powers, including the unilateral and counter-interventions of the superpowers during the Cold War and the reluctance of states to intervene in humanitarian crises.