premise: The American Civil War lasted 4 years.
hypothesis: The American Civil War was fought in the United States from 1861 to 1865 . The North and South quickly raised volunteer and conscription armies that fought mostly in the South over four years . 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 .