OXFORD, England — Because peacekeeping initiatives in postconflict countries are expensive and complex, and because the war in Iraq has undermined rich nations' belief in their likely success, a dispassionate look at the use of military intervention is timely.

A new study for the Copenhagen Consensus project that includes the first ever cost-benefit analysis of U.N. peacekeeping initiatives concludes that military might is an important tool for reducing bloodshed around the world.

Iraq is a misleading guide to the effectiveness of such initiatives. Unlike the vast majority of conflicts, its civil war was sparked by an international war. The far more typical scenario is political violence within a small, low-income, low-growth nation burdened with strong ethnic divisions.