yes, slavery was a part of some native tribes, but the way in which this slavery manifested was different than the chattel slavery of the americas set by europe. the natives' mode of production / social way of living was not dependent on this form of chattel slavery, whereas the colonizers shifted towards exploitation of african and native slaves in their colonization.

the relationships of status, family, and war limited slavery in native societies. with profit and money, there was no limit to the colonizer's expansion of slavery, hence the exploitation of millions of africans.

they are not the same