What is strikingly different in 1950 is that blacks overtake whites in their level of urbanization. After 1950, blacks become more urbanized than whites, and they continue to urbanize. Whites de-urbanized after 1970. Blacks moved to the cities after World War II, en masse. And it is after this move that severe family-formation problems began to emerge. The data suggest that the clues to recent family-formation problems among blacks are to be found in the circumstances of black urbanization after 1950.
Pointer from John Alcorn. The data in the paper show that before 1950, marriage rates of black women were even higher than those of white women.