During which conflict did the United States fight in the 1900s?

The correct answer, World War I, is significant because it marked a major engagement of the United States in global conflict during the 20th century. The war lasted from 1914 to 1918, with the U.S. entering in 1917 after years of neutrality. This entry had a crucial impact not only on the outcome of the war but also on the United States' role in international affairs moving forward. The war saw the U.S. join the Allies, which included major countries like France and the United Kingdom, against the Central Powers, leading to a shift in power dynamics in the world.

While the other conflicts listed also occurred during the 1900s, they are later events. The Korean War took place from 1950 to 1953, the Vietnam War spanned from the late 1950s to 1975, and the Gulf War occurred in 1990-1991. World War I set the stage for these subsequent conflicts and was pivotal in shaping modern geopolitics.