The trans-Atlantic slave trade was one leg of a three-part system known as the triangular trade. The forming of the triangle began when European ships, carrying firearms and manufactured goods, sailed to Africa, where the commodities were traded for enslaved men, women and children. Next, the same ships transported the human cargo across the Atlantic Ocean to the Americas.
This horrific journey was called the Middle Passage. Completing the triangle, the ships—having disembarked the enslaved Africans—were reloaded with cotton, sugar, tobacco and other cash crops produced by slave labor, and returned to Europe.
The countries that enslaved the highest number of Africans, from the most to the least, were Portugal, Britain, France, the Netherlands, Spain, the United States and Denmark
Another downplayed factor is the central role played by ruling African states in the capture and sale of fellow Africans to European traders—an estimated 90 percent of all captives. The main motivation behind these transactions was the acquisition of guns for use in inter-ethnic warfare. The enslaved were abducted from as far north as present-day Senegal to as far south as Angola, and transported to destinations as far south as Argentina and as far north as New England.