Rising tensions between major powers in Asia pose new risks to the region’s prosperity and stability, and possibly to international peace. Despite decades of rapid economic growth and social improvement in Asia, a flammable mix of still-bitter historical grievances, increasing resource competition, arms racing, and nationalist feeling—especially among the young—is fueling disputes such as those among China, Japan, and Southeast Asian nations over claims to tiny islands in the seas around China. As the United States “rebalances” to Asia, these geopolitical fault lines and flash points threaten to derail the Asian engines of global growth and involve the United States in irreconcilable regional rivalries and even military conflict.