Ordinary reading of your post suggests that "they" (in red) to whom you refer are black African (in red as well). If I misinterpreted your post, I do apologize.
Sorry I was unclear.
Both uses of "they" referred to "European culture", people as a group. They didn't invent slavery or slave markets. Those far predate the European technology advances that enabled a global slave trade. Technology that enabled lots of other human horrors as well.
The development of navigation equipment, reliably ocean crossing ships, and firearms made it possible for Europeans do things on a gigantic scale. Conquest, genocide, and slavery were extremely common and had been forever. They just took it to a new level. Europeans weren't notably more primitive(ethically) or brutal, but they were much better at ordinary human behavior. Which resulted in brutal colonial conquest, the Genocide of the Americas, and the African Diaspora.
My real point was that Africans as a whole weren't innocent victims. Of course, a profitable market for human merchandise encouraged a supply. Some individuals and tribes discovered that they could do very well for themselves by raiding their neighbors and selling them. But the bottom line is that there's plenty of blame to spread around.
If you're into blaming.
Tom