Did you know that the Persian Empire forbid slavery and promoted religious tolerance?

History is written by the victors. The Greeks had a lot of slavery and it is why the USA has slavery as well.

On the subject of history being written by the victors, slavery still persists in the USA on a massive scale in prisons as per the 13th Amendment.

In fact, as a result of mass incarceration and the 13th Amendment, US prison labor is the largest slavery operation in the world as we speak.