When do civil wars last especially long? Commitment problems can stymie conflict resolution but they are not homogeneous across all civil wars. Indeed, combatants’ perceptions of their adversaries significantly affect the severity of commitment problems. Intergroup interactions provide combatants with one crucial type of information about their adversaries and about the risks associated with signing a peace settlement, shaping strategic decisions. The argument is tested against a new data set of all ethnic civil wars between 1945 and 2004. The results demonstrate that intergroup interactions prolong wars when they indicate that a peace deal will be especially fragile or that the costs of it breaking down will be especially high. This is true, regardless of the combatants’ goals or their capabilities. In sum, information shapes perceptions and the severity of commitment problems, in turn affecting the duration of civil wars.