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

World War I is a significant conflict in U.S. history that took place from 1914 to 1918, with American involvement occurring from 1917 to 1918. The United States entered the war due to various factors, including unrestricted submarine warfare by Germany and the interception of the Zimmermann Telegram, which proposed a military alliance between Germany and Mexico. This war was pivotal as it marked the first time the U.S. played a major role in global military affairs, leading to significant political and social changes both domestically and internationally. The participation in World War I helped establish the U.S. as a world power and led to its involvement in subsequent global conflicts throughout the century.

In contrast, the other choices represent wars, but they either occurred before the 1900s, like the War of 1812, or fall outside the specified timeframe in the question. The Korean War (1950-1953) and the Vietnam War (1955-1975) were indeed important conflicts but occurred after the establishment of the U.S.'s role in World War I, making the latter the most representative answer for the 1900s.