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

World War I was fought from 1914 to 1918, and the United States joined in 1917. American troops helped the Allies in Europe, and the war ended in 1918 with an armistice.

World War II was fought from 1941 to 1945 after the United States entered following the attack on Pearl Harbor. The U.S. fought mainly in Europe and the Pacific, and the war ended with the defeat of Germany and Japan.

The Korean War was fought in the early 1950s during the Cold War. The United States led a United Nations force to help defend South Korea after North Korea invaded. The fighting ended with an armistice, and Korea remained divided into North and South.

The Vietnam War happened during the Cold War, when the United States tried to stop communism from spreading in Southeast Asia. It lasted for many years, with large numbers of U.S. troops sent in the 1960s and U.S. forces leaving in the 1970s. It had a big impact on American politics and public opinion at home.

The (Persian) Gulf War was fought in 1990–1991 after Iraq invaded Kuwait. The United States led a large international coalition to push Iraqi forces out of Kuwait. It was a major conflict near the end of the 1900s.