 The slave trade was largely a by-product of tribal and state warfare as a way of removing potential dissidents after victory or financing future wars.However, some African groups proved particularly adept and brutal at the practice of enslaving, such as Oyo, Benin, Igala, Kaabu, Asanteman, Dahomey, the Aro Confederacy and the Imbangala war bands.In letters written by the Manikongo, Nzinga Mbemba Afonso, to the King João III of Portugal, he writes that Portuguese merchandise flowing in is what is fueling the trade in Africans.