Notwithstanding its still relatively short life span and modest number of missions, the ESDP has already experienced serious difficulties in finding enough troops to man its military operations. This is not very surprising considering the significant costs military deployment generates for contributing states. It is however puzzling that some member states contributed a proportional share of the necessary troops despite these negative incentives, while others chose to free ride. This puzzle has remained largely underexamined in the burgeoning literature on the ESDP. The present study addresses this gap by examining the differences in contributions to operations EUFOR Congo and EUFOR Chad/CAR. It is argued that configurational analysis can contribute significantly to the literature on burden-sharing, which is used to derive an “incentives-constraints model”. This model is tested with Qualitative Comparative Analysis. Results of this analysis reveal that contrary to expectations derived from collective action theory, size is not a relevant condition to explain the share of burdens carried in ESDP military operations. The absence of other military deployments is revealed as a necessary condition, that leads to the outcome in three configurations. In the first two this necessary condition conjuncts with the absence of domestic constraints and either the presence of a strong peacekeeping tradition or a strong preference for the goal of the operation. In the third it conjuncts with peacekeeping tradition and a strong preference for the goal of the operation.
