The most accurate response regarding the effect of the Emancipation Proclamation on the Union's ability to fight the Civil War is:
It allowed the Union Army to recruit Black soldiers into the military.
The Emancipation Proclamation, issued by President Abraham Lincoln on January 1, 1863, declared that all enslaved people in Confederate-held territory were to be set free. This allowed the Union to recruit formerly enslaved individuals into the military, significantly bolstering the Union Army's numbers and contributing to its overall strength during the war.