The Civil War lasted almost exactly 4 years. According to civilwar.org approximately 320,000 Americans were killed.
Arguably the Civil War of the United States has been the most tragic war of American history because it tore apart the nation and left scars, some of which have still not healed, and because more Americans were killed in this war than in any other war in which the United States participated. Furthermore, it left every single family in the South with at least one male member dead; these American soldiers were also refused burial in Arlington National Cemetery.
This bloody war fought over tariffs (the South brought in 75% of the tariffs from ports that the Federal Government collected), trade, states rights, and slavery that many historians feel did not need to happen began on April 12, 1861, as Confederate batteries under the command of General Pierre G.T. Beauregard fired on Fort Sumter, a fort held by the Union in South Carolina. The war ended on April 9, 1865 when General Robert E. Lee and the Virginia army surrendered at the McLean House in the village of Appomattox.