Carl H. Nightingale, a professor of urban and world history at the University of Buffalo in New York is that rare academic who brings decades of research to life with the skill of a novelist. In “Segregation: A Global History of Divided Cities” (University of Chicago), he examines the ancient roots of the phenomenon and traces the idea of separating a “white town” from a “black town” to British rule in India in the 1700s. He pays particular attention to the mechanisms at work in Johannesburg and Chicago and manages to end on a hopeful note: Never before have so many people been engaged in efforts to end segregation.