China is a vast nation comprised of hundreds of distinct ethnic communities, each with its own language, history, and culture. Today the government of China recognizes just 56 ethnic nationalities, or minzu, as groups entitled to representation. This controversial new book recounts the history of the most sweeping attempt to sort and categorize the nation's enormous population: the 1954 Ethnic Classification project (minzu shibie). Thomas S. Mullaney draws on recently declassified material and extensive oral histories to describe how the communist government, in power less than...