Which war was fought by the United States in the 1900s?

The United States fought several wars in the 1900s, and World War I is one of the most significant. This global conflict lasted from 1914 to 1918, but the United States entered the war in 1917. The war was fought between the Allies, which included the United States, and the Central Powers. It was a pivotal moment in U.S. history, as it marked the country's emergence as a global power and involved significant mobilization of resources and troops.

The other wars mentioned, such as the Revolutionary War and the War of 1812, occurred in the 1700s and early 1800s, well before the 1900s. The Vietnam War, while a significant conflict for the U.S., fits within the latter half of the 20th century but is not as clearly identified with the broader shifts in the U.S.'s role on the world stage like World War I is. Therefore, World War I is the primary conflict that represents U.S. engagement in wars specifically within the 1900s timeframe.