Which war did the United States fight in the 1900s?

World War I is a significant conflict that the United States participated in during the 1900s, specifically from 1917 to 1918. This war marked a pivotal moment in global history, as it involved many countries and resulted in profound changes in the political landscape. The U.S. entry into the war was influenced by several factors, including unrestricted submarine warfare by Germany and the Zimmermann Telegram.

While other wars listed in the options, such as the Revolutionary War and the War of 1812, were important in American history, they occurred in the 18th and early 19th centuries, well before the 1900s. The Spanish-American War, although it took place in the late 19th century (1898), is also not within the designated range for this question. In contrast, World War I is distinctly tied to the early 20th century and represents a defining event of that era.