The northern elite also didn’t want to win at the start of the war: the union as it was, constitution as it is (with slavery that is). For the northern elite the south was a source of cheap cotton and an export market for finished goods, winning decisively would break that balance.

The end of slavery was truly a bottoms up movement, that forced the contradiction to be so great that it could not exist in one country.

John Dolan (aka the war nerd) has a great series on this subject on his podcast: Radio War Nerd.