Conventional wisdom suggests that biased military interventions in civil conflicts should increase the probability that the supported side will win. However, while this is the case for rebel groups, the same is not true for governments. The explanation for this surprising finding becomes clear once one considers the decision of a third-party intervener. Since interveners want to impact the outcomes of civil conflict, government- and rebel-biased interventions will be more likely when the government is facing a stronger rebel group. Given that government-biased third parties intervene in the “toughest” cases, empirically they appear to be less effective than rebel-biased interveners.