During the Jim Crow era many African Americans were excluded from the politics of by white politicians who believed that whites were inferior to black people and thought that they could make laws that limited African American rights.
Whites did not treat blacks as they were people. They dehumanized them and made them do all things they didn't want to do. They gave the blacks the worse jobs that they didn't want to do because they thought they shouldn't have the nicer jobs that whites had. They separated the two races by economic class which was not right.