What were the main causes of migration in the late eighteenth and early nineteenth centuries ?

The second significant cause of the Great Migration was the desire of black Southerners to escape segregation, known euphemistically as Jim Crow. Rural African American Southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the North.Jul 2, 2016

they remained in rural areas and worked at jobs such as lumbering or farming.

new evidence is discovered.

oversights and errors are corrected,

new technology is applied to evidence.