In past times, enslaving the populations of entire conquered nations or villages was common. Bringing slaves back to Rome was a regular part of an Army’s return. Enslaving one’s neighbors has been extremely common across the globe, since the beginning of humanity.

This is true, but not all Slavery is equivalent. All of it is obviously awful, but in the ancient world, conquering your neighbors provided an easy way to acquire more land and agricultural labor to feed a growing population of citizens. Enslaved people were not enslaved forever, and it was more akin to indentured servitude than chattel slavery. Rather, enslaved people would eventually be free, and become citizens of Rome, for instance, with more or less the same rights as any other citizen.

Chattel slavery, on the other hand, was inedibly unique, as far as historic slavery is concerned. People were now being enslaved, for life, based on the color of their skin, shipped off across a continent, and their descendants were also slaves upon birth, and those descendants were bought and sold as commodities on an open market.

Chattel slavery required the invention of modern notions of race to be invented, in order to justify it, which has had ongoing social impacts that extend far beyond the relations of production which birthed it.