The American Civil War was a civil war in the United States fought from 1861 to 1865. The Union faced secessionists in eleven Southern states grouped together as the Confederate States of America. The Union won the war, which remains the bloodiest in U.S. history. Among the 34 U.S. states in January 1861, seven Southern slave states individually declared their secession from the U.S. and formed the Confederate States of America. War broke out in April 1861 when they attacked a U.S. fortress, Fort Sumter. The Confederacy grew to include eleven states; it claimed two more states and several western territories. The Confederacy was never diplomatically recognized by any foreign country.