Black people in the United States are usually referred to as a more or less homogeneous group-by sociologists, newsmen, government officials, even their own leaders. But the history of black Americans is really the history of three distinct groups, whose descendants have very different incomes and occu- pations, and even different fertility rates, in the 20th century.
The first of these groups is the ante-bellum "free persons of color," who in the 1830s constituted 14 percent of the...