Here are some sources to help you with Africa's role in the Atlantic System:

From: http://www.nationalarchives.gov.uk/pathways/blackhistory/africa_caribbean/africa_trade.htm

Slaves for Guns

West African rulers were instrumental in the slave trade. They exchanged their prisoners of war (rarely their own people) for firearms manufactured in Birmingham and elsewhere in Britain. With their newly acquired weapons, kings and chiefs were able to expand their territories. The slave trade had a profound effect on the economy and politics of West Africa, leading, in many cases, to an increase in tension and violence.

Painting of 'The Slave Trade' by John Raphael Smith - opens new window

Europeans Repay African Hospitality
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List of forts under British control (extract) - opens new window

Black People and 'Mulattoes' Employed by the Royal African Company (162KB)
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In 1650, for example, Dahomey, a small coastal state on the Atlantic, extended its borders into the interior of Africa. Half a century later, the Asante Empire under Osei Tutu forcibly united a number of small kingdoms into a strong federation. A large proportion of the prisoners of war were sold on as slaves. Other Africans captured during raids into the interior were exchanged for commodities.