In MANY countries people of color X enslaved people of color X. So now - many generations later - no one knows anymore who was slave and who was master. So the term master is insignificant for the individuals in the country and dominantly associated with mastery in something.
So while technically the statement is correct, for the discussion here, many countries are not having an active discussion around slavery because it is no concern in the society because there are not slave-descendants (which are mistreated until today) vs. master-descendants.
No, if you read the article eitland posted (no judgment, I don't know) then you'd see that it was Muslims that was behind this slave trade.
One of their habits (or "innovations" in your terminology) that we don't often talk about was that of literally emasculating (in the literal sense) male captives.
This explains a whole lot of why there isn't a white population like the black in US.
Another explanation is that some where bought out from slavery by relatives in Europe.
You should read up on this.
You'll find that compared to the Arabic slave traders (that the Western slave traders sourced from), Western slave traders were kind of nice (edit: or smart, or less sadistic or something).
Oh, and their slave trade didn't end until much later, if ever. (Ever heard about how facilities for a certain sports event in Qatar were built?)
Why don't we talk about this? Sources are after all plentiful.
Edit: Let me add my guess: it doesn't fit the narrative that white, Christian men are worse than everyone else.
It also occurs to me that having these kinds of fights means people are running out of meaningful struggles, like we’re trying to wring out the last 5% and it gets inefficient because it starts doing harm as well. Then you see these hoaxes like Smollett and others and start thinking that the demand for egregious behavior exceeds supply in the US. It can happen, but it’s surprisingly rare given the state of conversation and rhetoric in this country.
Accountable implies a lot. But mindful we should be.