The American Civil War, also known as the War of the Rebellion, War Between the States or simply the Civil War, 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 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 Union and Confederate 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 US 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.