Name ONE war fought by the US in the 1900s.

The Vietnam War is indeed one of the wars fought by the United States in the 1900s. Specifically, it was a conflict that occurred primarily between the late 1950s and the mid-1970s, involving the U.S. in supporting the government of South Vietnam against the communist forces of North Vietnam. This war significantly impacted U.S. foreign policy, military strategy, and public opinion, marking it as a significant event in American history during the 20th century.

The War of 1812, the Spanish-American War, and the Revolutionary War all occurred before the 1900s. The War of 1812 was fought between 1812 and 1815, the Spanish-American War in 1898, and the Revolutionary War took place from 1775 to 1783. Therefore, while these wars are important in U.S. history, they do not fit the time frame specified in the question. The Vietnam War is the correct choice as it aligns with the requirement of being a conflict fought within the 1900s.