High Quality Content by WIKIPEDIA articles! The American Civil War (1861–1865) was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ("the Confederacy"); the other 25 states 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. Issues that led to war were partially resolved in the Reconstruction Era that followed, though others remained unresolved.