On January 1, 1863, Abraham Lincoln signs the Emancipation Proclamation. Attempting to stitch together a nation mired in a bloody civil war, Abraham Lincoln made a last-ditch, but carefully calculated, decision regarding the institution of slavery in America.

By the end of 1862, things were not looking good for the Union. The Confederate Army had overcome Union troops in significant battles and Britain and France were set to officially recognize the Confederacy as a separate nation. In an August 1862 letter to New York Tribune editor Horace Greeley, Lincoln confessed “my paramount object in this struggle is to save the Union, and it is not either to save or to destroy slavery.” Lincoln hoped that declaring a national policy of emancipation would stimulate a rush of the South’s slaves into the ranks of the Union army, thus depleting the Confederacy’s labor force, on which the southern states depended to wage war against the North.

READ MORE: What Abraham Lincoln Thought About Slavery

Lincoln waited to unveil the proclamation until he could do so on the heels of a Union military success. On September 22, 1862, after the battle at Antietam, he issued a preliminary Emancipation Proclamation declaring all slaves free in the rebellious states as of January 1, 1863. Lincoln and his advisors limited the proclamation’s language to slavery in states outside of federal control as of 1862, failing to address the contentious issue of slavery within the nation’s border states. In his attempt to appease all parties, Lincoln left many loopholes open that civil rights advocates would be forced to tackle in the future.

Republican abolitionists in the North rejoiced that Lincoln had finally thrown his full weight behind the cause for which they had elected him. Though slaves in the south failed to rebel en masse with the signing of the proclamation, they slowly began to liberate themselves as Union armies marched into Confederate territory. Toward the end of the war, slaves left their former masters in droves. They fought and grew crops for the Union Army, performed other military jobs and worked in the North’s mills. Though the proclamation was not greeted with joy by all northerners, particularly northern white workers and troops fearful of job competition from an influx of freed slaves, it had the distinct benefit of convincing Britain and France to steer clear of official diplomatic relations with the Confederacy.

Though the signing of the Emancipation Proclamation signified Lincoln’s growing resolve to preserve the Union at all costs, he still rejoiced in the ethical correctness of his decision. Lincoln admitted on that New Year’s Day in 1863 that he never “felt more certain that I was doing right, than I do in signing this paper.” Although he waffled on the subject of slavery in the early years of his presidency, he would thereafter be remembered as “The Great Emancipator.” To Confederate sympathizers, however, Lincoln’s signing of the Emancipation Proclamation reinforced their image of him as a hated despot and ultimately inspired his assassination by John Wilkes Booth on April 14, 1865.