Not often mentioned is the fact that there were Black slave owners. There is also little emphasis on the fact that it was Black tribal kings who sold Blacks to the slave ship captains for re-sale in US auctions.
Even after the trans-Atlantic slave trade was suppressed, slavery continued in many places in Africa, and even the European colonial powers (in control of most of black Africa from the 1880s on) had a hard time ending slavery. Of course it hasn't been ended totally even today in at least a couple of the Islamic countries in Africa.