Physicians have a motto that peacemakers would do well to adopt: "First, do no harm." Neither the United States nor the United Nations have quite grasped this. Since the end of the Cold War unleashed them to intervene in civil conflicts around the world, they have done reasonably well in some cases, but in others they have unwittingly prolonged suffering where they meant to relieve it.
How does this happen? By following a principle that sounds like common sense: that intervention should be both limited and impartial, because weighing in on one side of a local struggle undermines the legitimacy and effectiveness of outside involvement. This Olympian presumption resonates with respect for law and international cooperation. It has the ring of prudence, fairness, and restraint. It makes sense in old-fashioned U.N. peacekeeping operations, where the outsiders' role is not to make peace, but to bless and monitor a cease-fire that all parties have decided to accept. But it becomes a destructive misconception when carried over to the messier realm of "peace enforcement," where the belligerents have yet to decide that they have nothing more to gain by fighting.
Limited intervention may end a war if the intervenor takes sides, tilts the local balance of power, and helps one of the rivals to win - that is, if it is not impartial. Impartial intervention may end a war if the outsiders take complete command of the situation, overawe all the local competitors, and impose a peace settlement -