The Emancipation Proclamation was an order by U.S. President Abraham Lincoln to free slaves in 10 states. It applied to slaves in the states still in rebellion in 1863 during the American Civil War. It did not actually immediately free all slaves in those states, because they were still controlled by the Confederacy. It did, however, free at least 20,000 slaves immediately, and nearly all 4 million slaves (according to the 1860 United States census) as the Union army advanced into Confederate states. Until the Thirteenth Amendment to the United States Constitution in 1865, only the states had power to end slavery within their own borders. Lincoln issued the Proclamation as a war measure in his role as commander-in-chief.
The Proclamation made emancipation a goal of the Civil War. It also weakened efforts within England and France to officially recognize the Confederacy. As Union troops advanced into Rebel (Confederate) territory, they freed thousands of slaves per day. Many did not wait, but fled their owners to claim their freedom.
Five slave states (the Border States) had remained loyal to the Union and were not at war with the federal government. The Proclamation also did not apply to Tennessee, nor to areas within Virginia and Louisiana which Union forces already controlled.