They weren't allowed to read or to marry or to have control of their children, and were brutalized if they put a toe out of line. Amazing that the human spirit managed any rebellions, like Nat Turner, under such circumstances.
BTW, American slavery was more repressive than slavery as practiced in South America, where families were kept together as a rule, for instance, as the Catholic church insisted on marriage there.
I think only Muslims still practice slavery legally now.
They were probably treated more benevolently than any slaves in history. The Spartans treated their helots far more brutally, and the Romans also were much worse. Still the Helots and Roman slaves such as Spartacus, were constantly rebelling.
Nat Turner was a truly monstrous man. Nearly all the ones he killed were women and children.