The Emancipation Proclamation, issued by President Abraham Lincoln on January 1, 1863, was significant as it declared the freedom of all enslaved people in Confederate-held territory. Though it did not immediately free a single slave, it transformed the nature of the Civil War by adding a moral imperative to the Union's cause. The proclamation allowed African Americans to join the Union Army, which strengthened its numbers and resolve. Additionally, it signaled a shift towards eventual abolition nationwide, laying the groundwork for the Thirteenth Amendment, which formally abolished slavery in the United States in 1865.