The historical document that Abraham Lincoln issued to free the slaves was the Emancipation Proclamation. Announced on January 1, 1863, during the American Civil War, this executive order declared that all slaves in Confederate-held territory were to be set free. Although it did not immediately free all slaves, it marked a significant turning point in the war, transforming the conflict into a fight for liberation. The proclamation also allowed for the enlistment of African American soldiers in the Union Army, further strengthening the fight against slavery and influencing public sentiment regarding emancipation.