The exchange of peoples captured in local and ethnic wars within sub-Saharan Africa, the trans-Saharan slave trade with the Mediterranean Islamic world beginning in the seventh century, and the slave traffic across the Indian Ocean all testify to the long tradition and continental dimensions of the African slave trade before European intrusion. The enslavement of human beings was practiced in some form or another all over Africa — indeed, all over the world. Sanctioned by law and custom, enslaved people served critical and well-defined roles in the social, political, and economic organization of many African societies. Domestically these roles ranged from concubines and servants to royal guards and advisers. As was the case later in the Americas, some enslaved people were common laborers. In terms of economics, slaves were commodities for trade, no more or less important than other trade items, such as gold and ivory.
Over time, the trans-Saharan slave trade became less important than the transatlantic trade, which witnessed an explosive growth during the seventeenth and eighteenth centuries. The millions of enslaved Africans forcibly exported to the Americas had a lasting impact on African society and led ultimately to a wider use of slaves within Africa itself.