The basic logic of preventive diplomacy is unassailable. Act early to prevent disputes from escalating; reduce tensions that could lead to war; deal with today's conflicts before they become tomorrow's crises. Yet as we look at the record of these first years of the post-Cold War era, it is quite mixed. There have been some preventive diplomacy successes and opportunities that have been seized by major powers and international organizations to help preserve and protect the peace. But there...