From Wikipedia:
Vietnam War
"The war exacted a huge human cost in terms of fatalities (See: Vietnam War casualties), including 3 to 4 million Vietnamese from both sides, between 1.5 to 2 million Laotians and Cambodians, and 58,159 U.S. soldiers."
WWII Little Boy
On Monday, August 6, 1945, at 8:15 AM, the nuclear bomb "Little Boy" was dropped on Hiroshima by an American B-29 bomber, the Enola Gay, [17] directly killing an estimated 80,000 people. By the end of the year, injury and radiation brought total casualties to 90,000–140,000. [18] Approximately 69% of the city's buildings were completely destroyed, and about 7% severely damaged.
American Civil War
The American Civil War was one of the earliest true industrial wars. Railroads, the telegraph, steamships, and mass-produced weapons were employed extensively. The practices of total war, developed by Sherman in Georgia, and of trench warfare around Petersburg foreshadowed World War I in Europe. It remains the deadliest war in American history, resulting in the deaths of 620,000 soldiers and an undetermined number of civilian casualties. Ten percent of all Northern males 20–45 years of age died, as did 30 percent of all Southern white males aged 18–40. [3]