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.

Probably easy to convince someone its justifiable when life was so difficult.

Now we buy rotisserie chicken from Walmart, dump the trash in a landfill, and virtue signal people in the past who lived in a north korean style hellscapes.

I feel like creating an entire system dedicated to mass-murdering people industrially because of their origins or convictions is still the worst thing we’ve done as a species. Slavery is in the top spots, for sure, but it’s not “let’s create an industry solely dedicated to murder a specific ethnic group in the most efficient way possible” levels of crime against humanity.

Like, it has no economic benefits, it’s not for personal gain, it’s not because of lust or any human impulses, there is no reason to it apart from “let’s eradicate a part of humanity just because I said so”.

Yeah, but it wasn’t hereditary in Rome, lots of slaves did manage to achieve freedom, anyone could end up a slave and it was always a minority of the population. It was still messed up and they still abused them really badly or fatally at times, but it wasn’t as bad as the American style of slavery.

Sparta’s style was closer, though, and there’s other examples; it’s not like the system was without precedent. It also raise the whole question of the medieval and Arab slave trades. There isn’t really a good demarcation between them and the Atlantic trade, and of course they themselves would have roots in classical times.

Beyond slavery, there have been marauders like the Huns or the Khans, who would attack a city, and kill every single living thing, and then move on the the next one.

There’s reasonable evidence the Mongols, at least, liked to kill civilians, but you have to be careful about taking the historical accounts of their enemies at face value. Unlike in many wars between agricultural civilisations, they didn’t have literature of their own for us to draw from.

Trans-atlantic slavery was worse because it maximally exploited the humans as cattle. A quick death is much more convient than a lifetime of suffering.

rome wasn’t even physically capable of enslaving that many people as the african slave trade did.