Name one war fought by the United States in the 1900s.

The answer highlighting World War I or World War II is correct because both conflicts are significant wars in which the United States was actively involved during the 20th century. World War I occurred from 1914 to 1918, with the U.S. joining the Allies in 1917. World War II spanned from 1939 to 1945, with the U.S. becoming a principal member of the Allied Powers after the attack on Pearl Harbor in 1941. Both wars had profound impacts on global politics, economics, and society, reshaping the role of the United States on the world stage.

The Civil War, fought from 1861 to 1865, and the War of 1812, occurring from 1812 to 1815, both took place in the 19th century and therefore do not fit the criteria of being wars fought in the 1900s. The Korean War, which lasted from 1950 to 1953, is indeed a war in the 20th century; however, the inclusion of World War I or World War II makes it a broader and more encompassing answer, as these wars involved larger global coalitions and had a far-reaching impact on world history.