The Europeans who did most of the transportation of slaves from Africa viewed then as godless heathens.
It was a logistical god send because of the Colombian Exchange and advancement of sailing technology that allowed for Africa to become the in-between from Europe to South America.
They were a fairly easy "resource" to "harvest" because many warrior tribes inhabited Africa and would capture and sell their competing neighbors to the slave traders in exchange for rum and weapons/supplies.
The artist was most famous for his depictions of beautiful women from the tearooms, shops and pleasure quarters of Edo. He showed what life actually looked like in Edo through his art.