what caused west africans to transition from controlling the exchange of goods to european slave riders

There was an increase in demand for the slaves in the New World.

Explanation:

Historically, West Africa was producers of gold in the Middle Ages.  Portuguese became the first to exploit West Africa resources as they come across the gold in its region. European exchanged their products like cloth, utensils, weapons in return of gold, ivory, and stones. There was a transition from controlling the exchange of goods to European slave raiders. The West Africans became Europeans slave riders as they got rid of their enemies and received land, which was more wealth to them. Slavery was very much present in Africa before the arrival of Europeans. There was an increase in demand for slaves as the triangular trade was formed with the New World, Africa, and Europe. As European settlers began to settle in America, there was a demand for servent or worker for domestic help and in plantations.

number   5 i know this because savannah was the first capital and i took the test and all you have to do is look up a map of georgia savannah.