Most tribes had slaves before white people showed up, even chattel slavery. It might seem weird to white Americans who label both groups as disenfranchised minorities but no one at the time blinked at the idea. A racial heirarchy was established and while there were occasionally arguments the one thing most of the powerful people agreed on in America is that Africans were at the bottom of it and that meant everyone else had the “right” to enslave them.

What a lot of history leaves out is that part of the reason the indigenous people didn’t unify against white colonizers before it was too late is that in the early days native tribes were raiding each other for slaves and selling them to the whites, which would in turn spark wars between the tribes, ultimately weakening all parties and creating more war captives that would also be sold to the colonizers.

This further weakened the tribes, of course. Instead of war captives eventually being assimilated into the victors they were sold to colonizers, effectively reducing the native population’s manpower.

Until the 1750s there were even periods were more Native Americans from the continent were being sold in the Caribbean than African slaves. It wasn’t until the Indian Wars that this really changed as the tribes both became less willing to sell captives and European slavers decided natives could escape too easily compared to Africans.