Answer:
It was important to have popular support beforehand
Explanation:
It isn't a good answer tho. Lincoln wanted to strip the South of its labor force, and wished many of the slaves that were freed of the south would move to the North and unite with the Union Army. He needed some Union victories to make it more appealing, as the Northern armies were suffering after defeat. So after Antietam victory, he decided to issue the proclamation freeing the slaves that were in the South, but not the ones that were in the Northern "border" states. Such is life in politics.
