It was highly destabilizing. The existence of and furtherance of slavery creates a particular economic environment. The rapid decline of pre-colonial and early-colonial African polities in favor of either expansionist, extremely violent powers can be tied to the slave trade. The rise of Dahomey and the Segu Empire are perhaps the most famous example of this. (see Precolonial State in West Africa by J. Cameron Monroe for further information on Dahomey). But violent state-like authority was not the only outcome. Para-state authorities cropped up, especially aimed at enforcing debt and creating credit. Inevitably, these cycles of credit and debt, backed by para-state mafia-esque violence, created new opportunities but also contributed to destabilization. I bring up the opportunities because it is important to remember that this was not a uniform period of near-apocalypse decline. Living within the time, as with any period of rapid and destabilizing change, some benefited greatly. Where the Negroes are Masters by Sparks (as well as Making the State by Parker) is a great exploration of these dynamics, especially along the coastal regions. This is not to dismiss the enormous unquantifiable awfulness of the slave trade and its impacts or even assume the benefits were equal enough to offset the harm. However, to study African history in-of-itself, one has to realize that living within the period was far more ambiguous, even though with historical hindsight the trendlines are clear. The situation varied by region though, but ultimately the broad trend remained similar.

However, this was not necessarily driven by an exchange of slaves for manufactured goods. Toby Green in A Fistful of Shells, an outstanding book which anyone remotely interested in West Africa should read, argues fairly convincingly that the exchange featured non-manufactured goods, created a gross trade imbalance that, propped up by various factors local and foreign, economically stripped Africa for the benefit of Europeans, severely weakening the African economic situation. Manufactured goods were included, but perhaps not as solely dominant as used to be assumed.