Lincoln's Emancipation didn't free any slaves except those in states "in open rebellion." It was about turning the war into a moral platform on slavery so that no European power -- especially England, which had been waffling -- would dare come in on the side of the South. So it was less concerned with liberating slaves than it was about playing a powerful political trump card, one Lincoln had not dared play earlier lest he risk losing the "border states" like Kentucky and Missouri.
With the Union losing right and left and France and Russia giving serious thought to recognizing the Confederacy -- something they didn't risk doing without England's support -- Lincoln had to find some way to forestall the foreign intervention that would have tipped the war in the South's favor.
"Egalitarian" France and "enlightened" England could not justify entry into a war to defend human slavery.
In 1862, 90% of all slaves lived in those states "in open rebellion".
Iron Jack: "It was about turning the war into a moral platform on slavery so that no European power -- especially England, which had been waffling -- would dare come in on the side of the South."
Partially true.
But the larger reason was: the entire Confederacy consisted of only five million whites supported by nearly four million slaves.
So every Confederate slave freed and put to work for the Union was a two-fer -- South down one, North up one.
And abolition added another moral dimension to the war.
Therefore, even though abolition was not on the Republican 1860 platform, the logic of war made it a necessity.
You are right about France. But Russia was pro-Union throughout the war.