Greed,sub species,politics,business,cheap labor.pecking order.same reasons the rich get richer while the poor slide further down the scale. Even today.
They were forced from Africa to come work in the southern colonies. More specifically to work as slaves for white people or anyone who had the money. They were treated that way for a whole bunch of reasons I'm not even going to try and explain. People were a lot more racist back then. Not that racism doesn't exist cause Let me tell you, Some parts of my city you just don't go to (mostly at night ) if your a certain color. Even today racism still exists..Sad but true