Peacebuilding is successful in ending wars, but rarely leads to democratic postwar regimes. The peacebuilding literature typically explains this outcome by cooperation problems between the warring parties, by a lack of capacity within postwar society, or by underfunded and poorly coordinated missions. This paper provides an alternative explanation. It argues that the single most important factor explaining a democratic outcome is local demand for democracy. But elites in postwar countries only rarely demand democracy, because the adoption costs are too high. Adoption costs are low only when democratization is linked to a war for independence or when democracy is seen as a way out of a stalemate. Peacebuilders have only a limited impact on postwar democratization. They rarely use their leverage over local elites in order to push for democratic reforms, because they prioritize stability over democratic reforms. These arguments are tested using nine empirically thick case studies of recent peacebuilding missions.