I would be loathe to credit “liberals” with the issue of emancipation. Freeing innocent people from bondage is the antithesis of what the left is about.
They didn't initiate the war to emancipate the slaves. They initiated the war to keep Southern economic trade with Europe under the control of New York and Washington DC. When they began, the intent was simply to restore everything as it was prior to 1861. The effort to emancipate the slaves did not start until nearly two years after the war had began.
They ended up emancipating the slaves to wreck the South's ability to continue fighting the war, and to wreck them economically when the war was concluded. There was no actual milk of human kindness in any of their actions, it was all about asserting control from Washington DC.
Imposing a new morality especially with government forcing it down everyone's throat is a hallmark of Liberal methodology. More power to Washington DC is also a characteristic of Liberal thought.