I agree with all of this except (partly) your first point.

I hope you are OK with this rather long comment. If you would rather I not do so again, I won't.

You are an extremely educated and informed person so I doubt what I am going to say is stuff you don't already know, but I'm stating for the sake of argument...

Slavery existed for thousands of years. It existed in ancient China, India, Greece, Rome, the Americas, and, yes, Africa. Typically people enslaved those they conquered.

The Arabs had a thriving slave trade through Africa long before they started selling black slaves to Europeans. Many black chiefs sold slaves of defeated enemies as well. Which should not surprise us. Africa is an extremely diverse place. Blacks don't "all look alike" - they are more diverse than any other group.

Until relatively recently, however, race was not a huge factor when it came to slavery. Arabs took white slaves, Americans had both white and black indentured servants (who were both treated horribly). The first person killed in the American REvolution was Crispus Atticks, a free black man. (how horrible is it that we have to specify he was free?)

Very shortly after the American colonies formed, however, the face of slavery became exclusively black in this country and in other European colonies such as Jamaica and Brazil.

People all over the world are still living in what is, in practice if not in name, slavery. This includes blacks in places like Mauritania, but also little girls used as sex slaves in so-called civilized countries.

I really don't understand how anyone who has read the history of the Belgian Congo or has read of the exploitation of women in places like Great Britain can think that Europeans are superior to Africans.