The institution of owning human beings as property — one of the most widespread and durable institutions in human history, practiced on every inhabited continent, powering the ancient economies of Greece, Rome, and the Near East, and reaching its most systematic modern form in the Atlantic plantation complex that built the wealth of the early capitalist world — and one of the central subjects of moral and political philosophy, whose abolition required a reconception of what it means to be human.
Slavery is one of the few institutions that appears in every complex civilization in history — ancient Mesopotamia, Egypt, Greece, Rome, India, China, the Islamic world, pre-Columbian America, and the modern Atlantic world all practiced it. This universality is not a comfort. It means the question is not 'why did some people enslave others?' but 'why was enslaving people ever considered acceptable — and what had to change for it to become unacceptable?' What changed came remarkably late. Only in the last few centuries did people begin to insist that no human being can rightfully be owned — and then fight, against fierce resistance, to make that belief the world’s law.