While pre-colonial Africa, like all societies, had slavery, it was not anywhere near as severe as US plantation slavery or slavery elsewhere in the Americas. The only place in Africa that had anything close to what plantation slavery was like in the US was what is known as the kingdom of Dahomey.
Get used to me. Black, confident, cocky; my name, not yours; my religion, not yours; my goals, my own; get used to me. -Muhammad Ali