Answer: To end slavery in the Confederacy and weaken the Southern war efforts.
Step-by-step explanation:
President Lincoln issued the Emancipation Proclamation in 1863 and this freed all the enslaved people in the Confederacy. This was a very good move because it had multiple effects that weakened the war effort of the Confederacy.
Firstly it made the Civil War about ending slavery which dissuaded European powers from supporting the Confederacy as they had abolished slavery. It also led to tens of thousands of African Americans signing up for the Union Army because they knew that victory meant freedom for their race.