The American Civil War was a civil war in the United States between the Union (states that remained loyal to the federal union, or "the North") and the Confederacy (states that voted to secede, or "the South"). While the total death toll of the war is not fully known, it is generally agreed that it resulted in at least 1,030,000 casualties (3 percent of the population), including about 620,000 soldier deaths—two-thirds by disease—and 50,000 civilians. Some experts, including Binghamton University historian J. David Hacker, believe the number of soldier deaths was at least 750,000, and possibly as high as 850,000. The Civil War remains the deadliest military conflict in American history.