In the mid-fifteenth century, Portuguese ships sailed down the West African coast in a maneuver designed to bypass the Muslim North Africans, who had a virtual monopoly on the trade of sub-Saharan gold, spices, and other commodities that Europe wanted. These voyages resulted in maritime discoveries and advances in shipbuilding that later would make it easier for European vessels to navigate the Atlantic. Over time, the Portuguese vessels added another commodity to their cargo: African men, women, and children.

For the first one hundred years, captives in small numbers were transported to Europe. By the close of the fifteenth century, 10 percent of the population of Lisbon, Portugal, then one of the largest cities in Europe, was of African origin. Other captives were taken to islands off the African shore, including Madeira, Cape Verde, and especially São Tomé, where the Portuguese established sugar plantations using enslaved labor on a scale that foreshadowed the development of plantation slavery in the Americas. Enslaved Africans could also be found in North Africa, the Middle East, Persia, India, the Indian Ocean islands, and in Europe as far as Russia.

English and Dutch ships soon joined Portugal's vessels trading along the African coast. They preyed on the Portuguese ships, while raiding and pillaging the African mainland as well. During this initial period, European interest was particularly concentrated on Senegambia. Culturally and linguistically unified through Islam and in some areas, Manding culture and language, the region and Mali to its east had a long and glorious history, centered on the ancient Kingdom of Ghana and the medieval empires of Mali and Songhay. Its interior regions of Bure and Bambuk were rich in gold. It reached the Mediterranean and hence Europe from Songhay. The slave trade was closely linked to the Europeans' insatiable hunger for gold, and the arrival of the Portuguese on the " Gold Coast" (Ghana) in the 1470s tapped these inland sources.

Later, they developed commercial and political relations with the kingdoms of Benin (in present-day Nigeria) and Kongo. The Kongo state became Christianized and, in the process, was undermined by the spread of the slave trade. Benin, however, restricted Portuguese influence and somewhat limited the trade in human beings.

Starting in 1492, Africans were part of every expedition into the regions that became the American Spanish colonies. By the beginning of the sixteenth century, they were brought as slaves to grow sugar and mine gold on Hispaniola, and were forced to drain the shallow lakes of the Mexican plateau, thereby finalizing the subjugation of the Aztec nation. In a bitter twist, the Africans were often forced to perform tasks that would help advance the genocide that would resolve the vexing "Indian question."

Documents Illustrative of the History of the Slave Trade to America: Volume I: 1441-1700 by Elizabeth Donnan

By the middle of the seventeenth century, the slave trade entered its second and most intense phase. The creation of ever-larger sugar plantations and the introduction of other crops such as indigo, rice, tobacco, coffee, cocoa, and cotton would lead to the displacement of an estimated seven million Africans between 1650 and 1807. The demand for labor resulted in numerous innovations, encouraged opportunists and entrepreneurs, and accrued deceptions and barbarities, upon which the slave trade rested. Some slave traders - often well-respected men in their communities - made fortunes for themselves and their descendants. The corresponding impact on Africa was intensified as larger parts of west and central Africa came into the slavers' orbit.

	Slave Exports from Africa - The Atlantic Migration from Transformations in Slavery: A History of Slavery in Africa by Paul E. Lovejoy
	Nationality of Ships Engaged in the Atlantic Slave from Transformations in Slavery: A History of Slavery in Africa by Paul E. Lovejoy

The third and final period of the transatlantic slave trade began with the ban on the importation of captives imposed by Britain and the United States in 1807 and lasted until the 1860s. Brazil, Cuba, and Puerto Rico were the principal destinations for Africans, since they could no longer legally be brought into North America, the British or French colonies in the Caribbean, or the independent countries of Spanish America. Despite this restricted market, the numbers of deported Africans did not decline until the late 1840s. Many were smuggled into the United States. At the same time, tens of thousands of Africans rescued from the slave ships were forcibly settled in Sierra Leone, Liberia, and several islands of the Caribbean.