During its first 100 years of existence, more than 683,000 Americans lost their lives, with the Civil War accounting for 623,026 of that total (91.2%). Comparatively, in the next 100 years, another 626,000 Americans died through two World Wars and several more regional conflicts (World War 2 representing 65% of that total). Using this comparison, the Civil War might very well be the most costly war that America has ever fought. (Partial Sources: U.S. Army Military History Institute and iCasualties.org)