Freeing the slaves (a task which required us to fight the deadliest war in our history) was still the right and necessary thing to do. "You broke it, you bought it."
That's not what I'm asking for. In the US, Native Americans and descendants of slaves have full legal and political rights (in fact, Native Americans have extra political rights not granted to other citizens). Israel also can give Palestinians full legal and political rights, either in a separate state or as part of a one-state solution, without compromising its continued existence.