The significance of the Emancipation Proclamation was its role in transforming the American Civil War into a battle for freedom. Issued by President Abraham Lincoln in 1863, it declared the freedom of slaves in Confederate-held territory. This act aimed to weaken the Confederate war effort while also allowing freed slaves to join the Union Army, bolstering its numbers. It shifted the war's focus, emphasizing the moral cause of abolition alongside the military conflict, and paved the way for the eventual passage of the 13th Amendment, which abolished slavery.