The American Civil War, from 1861 to 1865, also known as the War Between the States and several other names, was a civil war in the United States of America. Eleven Southern slave states declared their secession from the U.S. and formed the Confederate States of America, the Confederacy. Led by Jefferson Davis, they fought against the U.S. federal government the 'Union', which was supported by all the free states and the five border slave states. The war, the deadliest in American history, caused 620,000 soldier deaths and an undetermined number of civilian casualties, ended slavery in the United States, restored the Union, and strengthened the role of the federal government. The social, political, economic and racial issues of the war decisively shaped the reconstruction era that lasted to 1877, and continued into the 20th century.