The American Civil War (1861–1865), often referred to as The Civil War in the United States, was a civil war fought over the secession of the Confederate States. In response to the election of an anti-slavery Republican as President, 10 southern slave states declared their secession from the United States and formed the Confederate States of America ("the Confederacy"); the other 23 states and 2 territories supported the federal government ("the Union"). After four years of warfare, mostly within the Southern states, the Confederacy surrendered and slavery was outlawed everywhere in the nation.