Trade between Europeans, Middle-Easterns and Africans of goods and people had been going on for centuries before the one to the US. I was not saying it was all based on the belief that one race was superior or on religious grounds. In most cases, it was Africans who sold Africans, so it wasn't being done for either of those reasons but probably purely for money. As in most situations, there are multiple sides to it.
The theory of one race being more evolved was around long before Darwin, Darwin's father wrote on it as well. Often the two views of both science and religion were entwined. Each one bolstered the other.
https://www.washingtonpost.com/loca...e6aef0-5aeb-11e9-a00e-050dc7b82693_story.html
Darwin simply made it popular
Darwin, race and gender
"he still divided humanity into distinct races according to differences in skin, eye or hair colour. He was also convinced that evolution was progressive, and that the white races—especially the Europeans—were evolutionarily more advanced than the black races, thus establishing race differences and a racial hierarchy."
He also wrote flattering things about women too.
"the formation of her skull is said to be intermediate between the child and the man”
Darwin 1871
It gave people a reason to keep slavery or mistreatment of other races as well as women going for 'real reasons', scientific ones.