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

One notable war fought by the United States in the 1900s is World War I, which occurred from 1914 to 1918. The U.S. entered the conflict in 1917, joining the Allied Powers against the Central Powers. This war was significant as it marked America's emergence as a global power, and it led to substantial changes in military strategy, international relations, and the political landscape both domestically and globally.

World War I is distinguished by its trench warfare, the introduction of new military technologies, and the profound social impacts it had on various nations, including changes to women’s roles and economic structures. The Treaty of Versailles, which formally ended the war, had lasting consequences that influenced international politics leading into World War II.

While World War II, the Korean War, and the Gulf War are also key conflicts involving the United States, the question specifically asks for a war fought in the 1900s, and World War I is an important historical milestone that signifies America's role in 20th-century global conflicts.