I am descended from slaves. So are you. From slave-owners, too. Given the history of the human race, it could hardly be otherwise.

Slavery was the normal form of social organization from the discovery of agriculture onwards. It may have been common among hunter-gatherers long before that, but the evidence is inconclusive. What we do know is that ownership of human beings is at least as old as civilization. The cities of Ur and Sumer, of Egypt and Persia, of the Indus Valley and Xia Dynasty China were built by forced labor.