There is a number of positions on the issue of the slavery impact on African society. Well, all of them concludes the negative (surprisingly, yeah?) influence on the economic and social development of Africans. One of the first, who started this discussion was Walter Rodney with his book How Europe Underdeveloped Africa. According to him, slave trade utterly transformed the African economy. It blocked the state-building and at the same time stimulated the slave traffic within the continent. David Eltis, on the contrary, claims that not all the Africans states were involved in the slave trade, but only the small share of them. Thus, it couldn’t provide a global effect on the whole continent. John Fage says that in a long perspective, slave trade rather stimulated the formation of political states and economic development. John Thornton states that the slavery was primarily the outcome of internal African problems. Such as including economic and political lopsided development.
There are a bunch of other researchers, who join the dispute. To get an understanding you can read some analytic paper on the topic, like this one.
If the theme is totally new to you, I’d recommend starting from this video.