Several studies show a beneficial effect of PKOs. However, by looking at individual effect pathways (intensity, duration, recurrence, diffusion) in isolation they underestimate the peacekeeping impact of PKOs. We propose a novel method to evaluate the combined impact across all pathways based on a statistical model of the efficacy of UN PKOs in preventing the onset, escalation, continuation, and recurrence of internal armed conflict. We run a set of simulations based on the statistical estimates to assess the impact of alternative UN policies for the 2001–13 period. If the UN had invested US 200 billion in PKOs with strong mandates, major armed conflict would have been reduced by up to two thirds relative to a scenario without PKOs and 150,000 lives would have been saved over the 13- year period compared to a no-PKO scenario. UN peacekeeping is clearly a cost-effective way of increasing global security.