what was the bloodiest one day confrontation in american history
1 Sept. 17, 1862, Battle of Antietam [Bloodiest calendar day on American soil, probably 4,300 killed that day.]. 2  Livermore, Numbers and Losses in the Civil War: 2,108 US + 2,700 CS [= 4,808]. 3  NPS. 4  KIA: 2100 USA + 1550 CSA = 3,650 killed in action on both sides.