From the 1520s to the 1860s an estimated 11 to 12 million African men, women, and children were forcibly embarked on European vessels for a life of slavery in the Western Hemisphere. Many more Africans were captured or purchased in the interior of the continent but a large number died before reaching the coast. About 9 to 10 million Africans survived the Atlantic crossing to be purchased by planters and traders in the New World, where they worked principally as slave laborers in plantation economies requiring a large work force. African peoples were transported from numerous coastal outlets from the Senegal River in West Africa and hundreds of trading sites along the coast as far south as Benguela (Angola), and from ports in Mozambique in southeast Africa. In the New World slaves were sold in markets as far north as New England and as far south as present-day Argentina. .
THE EARLY HISTORY OF EUROPEAN TRADE WITH AFRICA .
The marketing of people in the interior of Africa predates European contact with West Africa. A Trans-Saharan slave trade developed from the 10th to 14th century which featured the buying and selling of African captives in Islamic markets such as the area around present-day Sudan. A majority of those enslaved were females, who were purchased to work as servants, agricultural laborers, or concubines. Some captives were also shipped north across the deserts of northwest Africa to the Mediterranean coast. There, in slave markets such as Ceuta (Morocco), Africans were purchased to work as servants or laborers in Spain, Portugal, and other countries.
By the mid-1400s, Portuguese ship captains had learned how to navigate the waters along the West Coast of Africa and began to trade directly with slave suppliers who built small trading posts, or "factories," on the coast. European shippers were thus able to circumvent the Trans-Saharan caravan slave trade. The slave trade to Europe began to decrease in the late 1400s with the development of sugar plantations in the Atlantic islands of Madeira and Sao Tome.