A range of seemingly rival theories attempt to explain why some individuals take extraordinary risks by choosing to participate in armed conflict. To date, however, competing accounts have typically not been grounded in systematic, empirical studies of the determinants of participation. In this article, we begin to fill this gap through an examination of the determinants of participation in insurgent and counterinsurgent factions in Sierra Leone's civil war. We find some support for all of the competing theories, suggesting that the rivalry between them is artificial and that theoretical work has insufficiently explored the interaction of various recruitment strategies. At the same time, the empirical results challenge standard interpretations of grievance-based accounts of participation, as poverty, a lack of access to education, and political alienation predict participation in both rebellion and counterrebellion. Factors that are traditionally seen as indicators of grievance or frustration may instead proxy a for more general susceptibility to engage in violent action or a greater vulnerability to political manipulation by elites.