Exiting the Coalition: When Do States Abandon Coalition Partners during War?

When do countries abandon coalition partners during war? Prominent arguments about alliance dissolution focus on peacetime, yet the ability of alliances to inuence international politics ultimately hinges on their cohesion or dissolution during war. In this paper, I argue that battleeld circumstances heavily inuence the likelihood of defection from coalitions. First, countries ghting independently from their partners make attractive candidates for wedge strategies and hence are more likely to defect. Second, coalitions are more likely to collapse when it appears less likely that the coalition will triumph in the war as a whole. I test hypotheses about wartime developments statistically using new time-varying data on both front-level troop contributions and battle deaths. Consistent with theoretical predictions, countries are more likely to abandon coalition partners if they are ghting alone and when the coalition has fared worse in recent ghting.