After India and China, Indonesia was the biggest new nation-state to emerge in the mid-twentieth century. Consisting of thousands of islands large and small, it sprawls roughly the same distance as that from Washington, D.C., to Alaska, and contains the largest Muslim population on earth. Yet, on our mental map of the world, the country is little more than a faraway setting for earthquakes, tsunamis, and volcanic eruptions. The political traumas of post-colonial Egypt, from Suez to el-Sisi, are far better known than the killing, starting in 1965, of more than half a million Indonesians suspected of being Communists or the thirty-year insurgency in Aceh Province. Foreign-affairs columnists, who prematurely hailed many revolutions at the end of the Cold War (Rose, Orange, Green, Saffron), failed to color-code the dramatic overthrow,…