Claim: Ulysses S. Grant fought against Robert E. Lee.

The American Civil War was fought in the United States from 1861 to 1865 . After a long standing controversy over slavery and state 's rights , war broke out in April 1861 , when Confederates attacked Fort Sumter in South Carolina , shortly after Abraham Lincoln was elected . The nationalists of the Union proclaimed loyalty to the U.S. Constitution . They faced secessionists of the Confederate States of America advocating states ' rights to perpetual slavery and its expansion in the Americas .   Among the 34 U.S. states in February 1861 , seven Southern slave states individually declared their secession from the U.S. to form the Confederate States of America . The Confederacy grew to include eleven states ; it claimed two more border states -LRB- Kentucky and Missouri -RRB- , the Indian Territory , and the southern portions of the Union 's western territories of Arizona and New Mexico , which was organized and incorporated into the Confederacy as Confederate Arizona . The Confederacy was never diplomatically recognized by the United States government , nor was it recognized by any foreign country -LRB- although Britain and France granted it belligerent status -RRB- . The states that remained loyal , including the border states where slavery was legal , were known as the Union or the North .   The North and South quickly raised volunteer and conscription armies that fought mostly in the South over four years . During this time many innovations in warfare occurred , including the development and use of iron-clad ships , ultimately changing naval strategy around the world . The Union finally won the war when General Robert E. Lee surrendered to General Ulysses S. Grant at the battle of Appomattox , which triggered a series of surrenders by Confederate generals throughout the southern states . Four years of intense combat left 620,000 to 750,000 soldiers dead , a higher number than the number of American military deaths in World War I and World War II combined , and much of the South 's infrastructure was destroyed . The Confederacy collapsed , slavery was abolished and 4 million slaves were freed . The Reconstruction Era -LRB- 1863 -- 1877 -RRB- overlapped and followed the war , with the process of restoring national unity , strengthening the national government , and granting civil rights to freed slaves throughout the country . The Civil War is arguably the most studied and written about episode in American history .