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, after seven Southern slave states declared their secession and formed the Confederate States of America (the "Confederacy" or the "South"). (It ultimately included a total of eleven states.) 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. [ N 1 ] 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 civil rights to the freed slaves began. In the 1860 presidential election , Republicans , led by Abraham Lincoln , opposed the expansion of slavery into United States' territories . Lincoln won, but before his inauguration on March 4, 1861, seven slave states with cotton-based economies formed the Confederacy. The first six to secede had the highest proportions of slaves in their populations, a total of 48.8% for the six. [ 5 ] Outgoing Democratic President James Buchanan and the incoming Republicans rejected secession as illegal. Lincoln's inaugural address declared his administration would not initiate civil war. Eight remaining slave states continued to reject