This one is pretty much ASB territory, but an anti slavery clause is written into the constitution, and the southern states, mainly Georgia and the Carolina's, who were opposed to that OTL, actually go along with it. A true land of the free, without the scourge of slavery in its distant past. This down the line means a quicker civil rights movement, more job opportunities for freedmen, no bloody civil war, and a much more united America that can truly live up to being a land where all men are created equal. Not to mention such an America would likely be far more prosperous with it utilizing the whole of its population much earlier that OTL.