In Europe, slavery grew over centuries to be a vital and complex institution within the Roman Empire. There were various types and grades of slave, and established legal routes for slaves to gain their freedom. As the Roman Empire declined, so did slavery. The Church preached against Christians enslaving other Christians, and, throughout most of Europe, slavery was replaced with serfdom. The fact that the few slaves who existed were prisoners of war entrenched the idea of a strong racial and cultural difference between free Europeans and foreign slaves.

In medieval Africa, slavery was common, particularly in West Africa, where small kingdoms were continually coming into conflict with one another. When one of these kingdoms won a war, the winning side would enslave the losers. Though they usually kept these prisoners for labor on their own land, slaves were sometimes traded between kingdoms, or ransomed back to their homelands. There was no sense of Pan-African identity, so these slaves were all regarded as foreigners.

As early as the ninth century, a regular trade in slaves was established across the African continent to the Middle East. This trade was profitable enough for some kingdoms to focus on capturing members of neighboring states and tribes in order to participate in it. When the Portuguese set up trading posts on the West African coast in the late fifteenth century, it was, therefore, a natural step for their African trading partners to collaborate with them in what soon became the Atlantic slave trade.