We were talking about the form of slavery that was practiced legally in the USA: chattel slavery of black folks based in legal/scientific racism and counted as persons by the US Census.
 
Native American slavery had a little in common with the slavery written into the Constitution and common law, but . . . it did not share those characteristics: definition under common law and subject to the US Census. 

Or maybe it does. Gates didn't mention that and I don't really know it: were the slaves and free of First Nations enumerated by the US Census? I mean, they weren't really considered citizens. Did they count towards electoral votes and seats in Congress? 

From what I've seen, even the question of how many black folks were owned, under terms of US law, by The Civilized Tribes, is really vague and vexed. "As many as 10,000 at times" is what I've seen although I'm not sure where. That's why I added them and black slaveholders up to 1% of American slaves not owned by white folks.