How often did this happen vs Roman times? Before the dreadful US took over the South, slaves were much better treated and had way more upwards mobility, like in Florida when the Spanish and French were the colonizers. Places like New Orleans was much better for African descendants and many fled when they found out they’d be ruled by America.

I don’t cite Thomas Jefferson and his treatment of his slaves as the normative, in Roman times it was built into the system for slaves to buy their freedom and also have upwards mobility. That is not institutionalized for slavery in the US.