During the Civil War, African Americans tried to join the Union army of the north. They were told, "Keep out of this; this is a white man's war." At first President Lincoln said that the war was to save the Union, not to end slavery. But after a year he changed his mind. That is when he wrote the Emancipation Proclamation.
Lincoln wrote the Emancipation Proclamation in secret. To emancipate means to set free. A proclamation is an order to do something. The Emancipation Proclamation freed the slaves in all the states that had left the Union. President Lincoln thought the freed slaves would join the Union army. Many African American troops in the Union army wanted to fight in the war.
Lincoln's advisors asked him to wait for a victory in a battle before telling everyone about his new plan. They decided this so it would not look like the government needed blacks to save the Union.
President Lincoln waited three months until the Union army won an important victory at the Battle of Antietam. In 1862 Lincoln warned the Confederate States. He told them he would free their slaves if they did not return to the Union by January 1, 1863. The Confederates ignored him. So on New Year's Day in 1863, President Lincoln put his Emancipation Proclamation to work. He declared the slaves in all Confederate areas to be "forever free."