The south china sea is the most important body of water for the world economy—through it passes at least one-third of global trade. It is also the most dangerous body of water in the world, the place where the militaries of the United States and China could most easily collide. Chinese and American warships have just barely averted several incidents there over the past few years, and the Chinese military has warned off U.S. jets flying above. In July, the two nations carried out competing naval exercises in those waters. Given what is called the growing “strategic rivalry” between Washington and Beijing, the specter of an accident that in turn triggers a larger military confrontation preoccupies strategists in both capitals. These tensions grow out of a disagreement between the two countries as to whether the South China Sea is Chinese territory, a quarrel that speaks to a deeper dispute about maritime sovereignty, how it is decided upon, and the fundamental rights of movement in those waters.