Answer:
They had a devastating effect. Africa once had several thriving kingdoms along the outer-ring of the continent. Trade with western countries caused the population to decline as a whole, and many of these civilizations came to resent one another.
At the beginning, it had minimal effect on African society because they had more than enough slaves to give away in exchange for goods. These slaves were prisoners of war and there was a surplus of slaves. As the demand for slaves grew, African communities began to fight for the sole reason of capturing slaves to trade.
Slave hunts were commonplace and this caused both economic, and the cultural downfall of many African communities.
In an attempt to flee from abduction, many communities distanced themselves as much as possible from slavers. This caused an overall regression in technological advancement and reduced friendly relations between African communities.
The result was that Africa as a whole went from a world power to a large countryside filled with tribes fighting one another for dominance.