The American Civil War has the highest number of fatalities
The American Civil 
War, with involvement years from 1861 to 1865, resulted in the most significant number of U.S. military fatalities, totaling 
620,000. This figure surpasses the fatalities of World War II, which are the second highest, by 
214,601 casualties.
World War II ranks second in U.S. military fatalities
World War II, spanning from 1939 to 1945, saw 
405,399 U.S. 
military fatalities, making it the second deadliest conflict for the United States after the American Civil War.
The Gulf War had the fewest U.S. military fatalities
With only 
258 U.S. military fatalities, the Gulf War (1990-1991) experienced the lowest number of deaths among the major wars listed, highlighting the significant variance in U.S. military casualties across different conflicts.
Vietnam and Korean Wars combined fatalities
The Vietnam War (1965-1973) and the Korean War (1950-1953) together resulted in 
94,725 U.S. military fatalities, demonstrating the heavy toll of Cold War-era conflicts on American forces.
Increase in fatalities from the Revolutionary War to the Civil War
Fatalities surged from 
25,000 in the American Revolutionary War (1775-1783) to 
620,000 in the American Civil War, reflecting a dramatic escalation in the lethality of conflicts involving the 
United States over time.
20th-century wars' impact on U.S. military fatalities
The combined fatalities of World War I (
116,516) and World War II (
405,399) amount to 
521,915, underscoring the significant impact of global conflicts in the 20th century on U.S. military losses.
Wars in the 19th century versus the War on Terror
The Mexican-American War (1846-1848) and the War of 1812 (1812-1815) together accounted for 
33,283 fatalities, which is significantly lower than the fatalities from the War on Terror (2001-present) at 
7,078, highlighting changes in the nature and duration of U.S. military engagements.
The Spanish-American War's relatively low fatality rate
With 
2,446 fatalities, the Spanish-American War (1898) stands out for its relatively low number of U.S. military 
deaths compared to other conflicts, despite its significant historical impact.