What was a primary reason for the great migration of African Americans to northern cities during World War

The Great Migration was a massive movement of African Americans out of the South and into the North during the World War I era, around 1914-1920. Blacks moved to northern cities for the economic opportunity afforded by war conditions, but also to flee the overt racism and prejudice endemic in the South.

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.