Of course, the major impact of the slave trade was on the individual Africans who were caught up in it. They were taken and sold into slavery where the best they could hope for was a decent owner in a land thousands of miles from their families and everything they had ever known.
On a larger scale, the Atlantic slave trade affected African societies. It helped to enrich the rulers of the states that existed along the coast of West Africa (north of the Congo River and south of the Sahara). It did this because the Europeans paid these rulers for permission to set up trading posts and/or for slaves that the rulers captured.
The inland societies were the ones who were hurt the most by this trade. The coastal societies went inland to get slaves from the tribes that lived there. Those tribes and states were affected by having large numbers of people in the prime of life taken away from them. This harmed them economically, socially, and culturally.
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Many of them were captured and put on ships to be sent out. Life conditions in the ship were horrible. Most of them died in the ship. As more and more African Americans were being captured, small states begin disappearing.