Irrelevent..
Slavery was a world-wide practice..
Likewise, the first encoded laws, by Hammurabi, included an entire section dealing specifically with slavery, both voluntary and involuntary, and including the rights of slaves..
Slavery is a horror that has cursed the entire world since prehistoric times. It is present in the world today. Greek Civilization, that we love to admire, was based on slavery. So were Chinese, African, and Aztec; it's not only Western, you know.