On September 22, 1862, Abraham Lincoln issued the preliminary Emancipation Proclamation, declaring that on January 1, 1863, all persons held as slaves within any state in rebellion against the United States would be then, thenceforward, and forever free. It was a war measure, issued under the president's power as commander in chief, and it applied only where the Union government had no authority to enforce it.
He had written it in July and had been told to wait. When Lincoln read his draft to the cabinet on July 22, Seward objected that issuing it after a string of Union defeats would look like the last resort of a government on the ropes, and would be read abroad as a call to servile insurrection. Lincoln put the paper in a drawer and waited for a victory. Antietam on September 17 was not a clear one, but Lee had retreated and the invasion had failed. That was enough.
What the proclamation did was narrow and what it meant was broad. It exempted the slave states that had stayed in the Union, and it exempted the parts of the Confederacy already under Union control, on the argument that the government could seize enemy property used to wage war and could not constitutionally take property from loyal citizens. That is why it is often called an act that freed no one. It is also why the Thirteenth Amendment followed in 1865.
It changed the war abroad. British and French recognition of the Confederacy had been a real possibility in 1862, and the cotton famine in Lancashire had put pressure on the government. After September 22 no British ministry could recognise a slaveholding state, because the working-class organisations that had been campaigning for the Union had the argument. Palmerston and Russell dropped the idea of mediation in October.
It changed the army too. The proclamation said that black men of suitable condition would be received into the armed services, and about 180,000 did serve, in the United States Colored Troops, nearly a tenth of the Union army, most of them formerly enslaved. They were paid less than white soldiers until Congress fixed it in June 1864, and those captured at Fort Pillow in April 1864 were killed by Forrest's men rather than paroled.
The final proclamation came on January 1, 1863, and named ten states. It did not free anyone in the border states or in Tennessee or in the occupied parts of Louisiana and Virginia, and those people were freed by state action or by the Thirteenth Amendment. Juneteenth, the day the news reached Galveston, was June 19, 1865.