When "slavery" is mentioned in this context (wrt. black/white), it's reasonable to assume the person means it predates the Atlantic slave trade, which was not the only form of slavery, but it was the largest (and most visible) form of slavery involving predominantly white people owning predominantly brown people.

I make no claim over the validity of "white going first" predating the Atlantic slave trade, however. I simply don't know.

Yes, thank you very much. Fixed.