The Spanish and Portuguese and their American territories saw the disembarkation of almost two-thirds of all the enslaved carried from Africa. They were the first colonizers of the Atlantic and chose those areas that were best for obtaining slaves and putting them to work in the Americas. Almost every port large enough to launch a transoceanic voyage at some point entered the slave trade. Rio de Janeiro and Bahia (now Salvador) dispatched more vessels to Africa than did any European port, and overall sent out more voyages than did Europe. Thus the typical slave-trading voyage was not triangular, but rather bilateral. The Americas were the center of the slave trade because of their millennia-long isolation from the rest of the world, the inability of their Indigenous populations to resist Old World pathogens, and the very high land–labor ratios that resulted. Voyages to Africa from the Americas were quicker than those from Europe and the plantations and mines quickly generated a pool of investors willing to underpin the slave trade. In Brazil, especially, these small investors included free and enslaved Blacks, including even some enslaved crew. Close to half the merchandise traded for slaves came to be produced in the Americas rather than in Europe.

The Northwest Europeans were latecomers to Atlantic slavery and had to make do with second-best trading locations. It was the sixteenth- and seventeenth-century economic growth of the English and Dutch that allowed them to break into the Iberian Atlantic system rather than the two countries needing the slave trade to stimulate their economic development. Northwest Europeans never broached the Portuguese strongholds of Guinea-Bissau and Angola as slave-supply centers and were able to use Brazilian gold to hold their own in the Bight of Benin. And the British and the Dutch sold many of the slaves that they did buy to the Spanish Americas. The British made repeated unsuccessful attempts to break into the Brazilian market. The traffic was widely supported in most European countries, given that preparation for a successful voyage absorbed a large labor force and many thousands of investors.