No they weren't members of the tribe they were slaves. The Indians practiced chattel slavery. Then there were the Black slave owners. The Arab traders and the African tribes that sold captured Africans to the White Europeans.
The problem with racist like yourself is you focus on white people to the point of ignoring the same attitudes and problems of other groups. Of course I don't condone slavery I think it's a disgusting practice that needed to be stamped out then and needs to be abolished in places it's still used, like in modern day Africa.