Well, the colonists needed someone to do the work. Originally they had indentured servants, who would work for so many years to obtain their freedom. Then the colonists tried to enslave the Native Americans and that didn't work because the Native Americans knew the land and escaped. So, they decided to import blacks from Africa who weren't familiar with the land to do the hard labor for them. On top of that some of the white slave owners did not have the obligation to pay them for their labor. Hopefully, this helps.
