How did the slave trade cause a power shift in Africa?

By helping supply the Europeans with the slave trade, the rulers of certain African states were able to increase their power by acquiring more slaves for themselves.

The slave trade also transformed the existing states and societies in Africa. As states sought to expand at the expense of their neighbors, instability and warfare came about. The military became important. The slave trade became an extension of African politics. African governments in the enslaving societies became more centralized while the those who bore the brunt of the slaving attacks became anti authoritarian.

There was also a shift in the locus of power. Before the Europeans, the powerful African states were those that were in central Africa and could influence the trans-Saharan trade routes. Once the Europeans arrived, the power shifted to those states which were closer to the coast.