Your challenge, should you choose to accept it, is to come up with the least bloody way for the Union to with the American Civil War. Least bloody includes total military casualties on both sides.
There are a couple of important caveats:
(i) the PoD must be after 20 May 1861, i.e. after North Carolina votes to secede from the Union.
(ii) the Union victory must still result in the abolition of slavery within a reasonable timeframe after the war's end (say maximum of 8-10 years). It doesn't necessarily require much emancipation directly in the war itself, but eventual abolition must be a consequence of the Union victory.