THE PROMISED LAND
by Nicholas Lemann
Knopf; 410 pages; $24.95
There were two great migrations that transformed America in this century. The first brought millions of arrivals through the gates of Ellis Island. The second, which began in the 1940s, saw more than 5 million blacks move from the farms and small towns of the South to the cities of the North. Because it took place entirely within U.S. borders, that second massive relocation slipped by with less notice than the first, until the nation woke to find itself transformed. By the time their numbers had tapered off, around 1970, many...