Answer: B is correct.
Explanation: example of that: USA between two wars is sometimes described as a country practicing policy of isolationism (Harding, Coolidge, Hoover). ...especially in relation to Europe.
B) It helped to create a common culture in the United States.
African Americans settled in the slum and ghettos of the Northern side changing the demographics of the cities.
Explanation:
Places like Harlem in New York and Compton in California where there were very low income areas settled by predominantly black people in otherwise bludgeoning economies where they became slums is a characteristic of this migration.
As the north did not discriminate as much against the black population they moved over to their side and then they had not enough resources to live their lives well so they lived in the slums they had made.
These slums would remain the usually economically backward areas of the US for long.
