It is quite possible the first black slave in America was enslaved by another black. Certainly, most of the Greek slaves were other Greeks.
Kiev was likely a Viking slave trading center. Russ is a Scandinavian word, brought by the Vikings whose trade in Slavs gave us the word slave.
Nearly every major city in Ireland, including Dublin, were founded as Viking slave trading ports. The tribes of Ireland were constantly at war with one another, and whenever one prevailed, they would sell off the losers as slaves.
And keep in mind the Jews were slaves at one time. They never forget it, and this memory perhaps in part explains their cultural resiliency.
Most of what we know about the Roman Republic comes to us from a Greek slave, Polybius.
Blacks have no monopoly on having been slaves. We need to treat people as individuals. There is no such thing as a “group”. There is no such thing as a “class”. These are linguistic fictions created by and for short sighted and stupid intellectuals. They are not without use, but like anything else quickly become pernicious when taken too far.