The Europeans weren’t going to conquer Africa before they realize they needed able bodies to do labor, Such as cotton Pickin and cutting sugar cane......
So it wasn’t necessarily a thought in their head before then .
Honestly I think it's because the polls said clinton was gonna win by a landslide so I think people got comfortable. pollsters call people and ask who they're voting for and I don't think many people want to admit they're voting for someone like trump so the numbers were wrong.
Become a citizen is the answer
Inheritance, trade, sold slaves.
Hope this helped.
