Answer:
During the Civil War, Union policy towards slavery evolved significantly. Initially, the war was about preserving the Union, not abolishing slavery. However, as the war progressed, Lincoln issued the Emancipation Proclamation in 1863, which declared slaves in Confederate territory to be free. This marked a shift towards using emancipation as a war measure to weaken the Confederacy.
Additionally, the Union victory at Gettysburg in 1863 and the passage of the 13th Amendment in 1865 ultimately led to the abolition of slavery in the United States.