Why do similarly sized peacekeeping missions vary in their effectiveness to protect civilians in conflicts? We argue that peace operations with a large share of troops from countries with high-quality militaries are better able to deter violence from state and non-state actors and create buffer zones within conflict areas, can better reach remote locations, and have superior capabilities – including diplomatic pressure by troop contributing countries – to monitor the implementation of peace agreements. These operational advantages enable them to better protect civilians. Combining data from military expenditures of troop contributing countries together with monthly data on the composition of peace operations, we create a proxy indicator for the average troop quality of UN PKOs. Statistical evidence from an extended sample of conflicts in Africa and Asia between 1991 and 2010 supports our argument.