The American Civil War, also known as the War Between the States, or simply the Civil War in the United States (see naming), was a civil war fought from 1861 to 1865 in the United States after seven Southern slave states declared their secession and formed the Confederate States of America (the "Confederacy" or the "South"). The states that remained in the Union were known as the "Union" or the "North". The war had its origin in the fractious issue of slavery, especially the extension of slavery into the western territories. Foreign powers did not intervene. After four years of bloody combat that left over 600,000 soldiers dead and destroyed much of the South's infrastructure, the Confederacy collapsed, slavery was abolished, and the difficult Reconstruction process of restoring national unity and guaranteeing rights to the freed slaves began.