The long-awaited new book by the author of the bestselling All Our Kin is a poignant saga of a reverse exodus: the return of half a million black Americans to the rural South.There have been many books focusing on the black migration out of the South into Northern cities. But few people are aware that over the past 20 years the trend has been in the other direction, with African-Americans moving back south, to some of the least promising places...