Which factor would have had the least impact in causing the so-called "great migration" of african americans in much of the 20th century?

The correct answer is:

Jim Crow laws banning African-Americans from most types of employment in the South.

The Great Migration of the 20th century was the movement of large numbers of southern African Americans from the rural south to northern and western cities. This migration had little to do with Jim Crow laws banning African-Americans from work in the South. The main reason was the increasing job opening due to industrial growth in northern cities.  

because the earth is a round globe. but that is just what they tell us it is flat and those dudes actually where lying they sailed east.