Forming a military coalition during an international crisis can improve a state’s chances of achieving its political goals. We argue that the involvement of a coalition, however, can have unintended adverse effects on crisis outcomes by complicating the bargaining process and extending the duration of crises. This argument suggests that crises involving coalitions should be significantly longer than crises without coalitions. However, other factors that affect crisis duration are also likely to influence coalition formation. Therefore, taking into account the endogeneity of the presence of a coalition is essential to testing our hypothesis. To deal with this inferential challenge, we develop a new statistical model that is an extension of instrumental variable estimation in survival analysis. Our analysis of 255 post–World War II interstate crises demonstrates that, even after accounting for the endogeneity of coalition formation, military coalitions tend to extend the duration of crises by approximately 284 days.