American Civil War, also called War Between the States, four-year war (1861–65) between the United States and 11 Southern states that seceded from the Union and formed the Confederate States of America. The war resolved two fundamental questions left unresolved by the revolution: whether the United States was to be a dissolvable confederation of sovereign states or an indivisible nation with a sovereign national government; and whether this nation, born of a declaration that all men were created with an equal right to liberty, would continue to exist as the largest slaveholding country in the world.