We simulate how a set of different UN policies for peace-keeping operations is likely to affect the global incidence of internal armed conflict. The simulation is based on a statistical model that estimates the efficacy of UN peacekeeping operations (PKOs) in preventing the onset, escalation, continuation, and recurrence of internal armed conflict. The model takes into account a set of important conflict predictors for which we have projections up to 2035 from the UN and the IIASA. The estimates are based on a 1970–2008 cross-sectional dataset of changes between conflict levels and new data on PKO budgets and mandates. The simulations show a strong effect of PKOs on the global incidence of major conflicts, although restricted to operations with robust mandates. Extensive use of ‘transformational’ PKOs can reduce the global incidence of the most lethal conflicts with 65%.