Final answer:
Job opportunities in Northern cities were the primary condition responsible for the migration of African Americans from the South after the Civil War, leading to the urban population changes.
Step-by-step explanation:
The condition in society that was primarily responsible for the change in urban population of African Americans in several cities after the Civil War was the availability of job opportunities in Northern cities. The period known as the Great Migration saw a mass movement of African Americans from the rural South to the urban North, seeking industrial work and a reprieve from the segregation and racial discrimination prevalent in the South. Cities like Chicago, New York, and Detroit became major destinations as they offered jobs in industries such as steel, mining, shipbuilding, and automotive. Although the North also harbored racism and segregation, the economic opportunities there were significantly greater, leading to the dramatic population increases shown in the table.