Henri Christophe
L'empereur
In order to create trade between Africans and Europeans in the triangular slave trade it could be add civs as Ashante, Dahomey, Oyo, Benin, Kongo and Ndongo.I have nothing against black civilizations, indeed, slavery can be an excellent mechanic, but you have to create trade, of slaves between Africa and the Americas, the CIA called golden triangle : slaves, for gold, colonial products, gold, slaves, the birth of colonial leaders, even non-black in the independence of South American and post-colonial African and colonial nations, in general . You could put for minority populations forms of discrimination
But I can't see how to introduce discrimination in a game as Civilization. But it could be distinct a slavery mechanic in a lot of ways, without add ethnics to the static of the game, but a enslaved pops of a city could retain their faith, that's should force the player to spawn missionaries in it's own cities if they decided to enslave people of different religion.
Other way to do a playable discrimination is to have some policies as Apartheid, who the AI of the game should try to vote to abolish this policy when ONU is made.