The post–Cold War international order has promoted a “standard treatment” for civil wars involving the use of mediation to end conflicts and the deployment of peacekeeping forces to implement the resulting settlements. The United Nations has played a leading role in applying this standard treatment, which enjoys broad international support. By contrast, Western efforts to promote more robust humanitarian intervention as a standard response to civil wars remains controversial. While effective in relatively permissive postconflict environments, international mediation and peacekeeping efforts have proved insufficient to resolve harder cases of civil war, such as those in South Sudan and Syria. The UN has struggled to make the standard treatment work where governments refuse to cooperate or low-level violence is endemic. Growing major-power tensions could now undermine the post–Cold War regime for the treatment of civil wars, which, for all its faults, has made a significant contribution to international order.