International peacebuilding can improve the prospects that a civil war will be resolved. Although peacebuilding strategies must be designed to address particular conflicts, broad parameters that fit most conflicts can be identified. Strategies should address the local roots of hostility, the local capacities for change, and the (net) specific degree of international commitment available to assist sustainable peace. One can conceive of these as the three dimensions of a triangle whose area is the “political space”—or effective capacity—for building peace. We test these propositions with an extensive data set of 124 post–World War II civil wars and find that multilateral, United Nations peace operations make a positive difference. UN peacekeeping is positively correlated with democratization processes after civil war, and multilateral enforcement operations are usually successful in ending the violence. Our study provides broad guidelines for designing the appropriate peacebuilding strategy, given the mix of hostility, local capacities, and international capacities.