The transatlantic slave trade was one of the earliest international trade networks. It was organized as follows:
1) Europe to Africa
Merchants from Western Europe would load weapons, gunpowder, pearls, textiles, and other manufactured goods into ships. The ships would set sail to Africa where the merchants would exchange the goods for slaves.
2) Africa to America
Once the European merchants received the slaves, they would sail across the Atlantic ocean to the Americas and go sell the slaves to farmers for agricultural produce.
3) America to Europe
The merchants would then return with the agricultural produce to Europe and sell it to the locals.
Who Controlled Each Aspect?
The Europeans controlled most of the trading on the transatlantic slave trade. Most of their ships were used to transport the slaves and goods. However, the African elites and American farmers and traders also controlled the exchange of goods. The African elites ensured that the slaves were always available when the Europeans arrived, while the American entrepreneurs guaranteed the availability of agricultural products.
There are several different ways of looking at the slave trade, but one of the most common descriptions of it is the triangular trade. European merchants brought goods to Africa to trade with the Africans who controlled the slave trade in Africa. They traded these goods for slaves which they then brought to the Americas and traded for cotton, sugar, rum and other goods from the Americas that were generally produced with slave labor. The merchants then returned to Europe bearing the goods from the Americas.
The Africans generally controlled the actual slave market, bringing in captives from tribal warfare as well as from traders who specailzed in simply capturing people for slavery.
The Europeans dominated the other aspects of the trade because they dominated the shipping trade.