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

World War I is the correct choice because it was a significant conflict that involved the United States directly during the 1900s. The U.S. entered the war in 1917, joining the Allies against the Central Powers. The participation in World War I marked a crucial point in U.S. history, influencing both domestic policy and international relations.

In contrast, the other wars listed are not from the 1900s. The Civil War took place between 1861 and 1865, while the Revolutionary War occurred from 1775 to 1783. The War of 1812 was fought from 1812 to 1815. Therefore, World War I is the only option that fits the criterion of a war fought by the United States in the 20th century.