“Surviving the Crackdown in Xinjiang” is a expansive and detailed account of Xi Jinping’s policies against ethnic Uyghurs and Kazhaks in China’s northwestern region, which culminated in the detainment of a group estimated to number more than a million, in the largest civilian internment since the Holocaust. The staff writer Raffi Khatchadourian tells David Remnick how Xi Jinping’s government used an obsession with what it calls stability, and a fear of separatism and terrorism, to justify a campaign of genocide. It involves forced cultural assimilation, mass imprisonment, and coercive measures to reduce the birth rate.