I wonder which were the largest "institunalized" slavery cases over the ages (if one vaguely define slavery as being forced or fooled to do work in harsh condit

I wonder which were the largest "institunalized" slavery cases over the ages (if one vaguely define slavery as being forced or fooled to do work in harsh conditions supported by the local rulers/govs, without the ability to stop - something like that, common sense). I think African slavery was large, but there were Romans and Greeks before, or Asian countries. Pretty much everyone I guess. I am asking this question because when I recently discussed massive homicides, I has the Nazi camps in mind and a friend mentioned Pol Pot's as being much bigger. The place you are in (France in my case) biaises this a lot.