Can the polarization between Democrats and Republicans in the U.S. be reversed?

[Angrboda]

The north wanted to keep the south and free the slaves. They kept the south but did not free the slaves. And the reason was the concessions they gave.

Anyway, as pointed out, even if you are right in the specific case, that wouldn't mean you are right in the general case. That the north also gained something by those concessions, the concessions were necessary to accomplishing the goal of continued peace in the union, as even you admit. So your point appears somewhat Pyrrhic even if true, as the question is how are such stabilities achieved, and in this case the answer is concessions. That you feel the north had liberty in dispensing such concessions and that achieving their ends was facilitated by concessions does not rebut the point that concessions on the part of the north were a required element of the solution, not simply an optional bonus. So my overall point is abetted. If the north hadn't made those concessions, then peace may not have lasted, or, at minimum, the union would have become a union in name only.