Name one war fought by the United States 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 involved many of the world's great powers and was known for its unprecedented scale and devastation. The U.S. entry into the war was prompted by several factors, including the interception of the Zimmerman Telegram and unrestricted submarine warfare by Germany.

World War I was crucial in shaping modern international relations and led to the establishment of organizations like the League of Nations. Its outcomes also set the stage for major geopolitical changes in the following decades, influencing events leading up to World War II. Understanding the involvement of the United States in World War I is key to grasping the broader context of American history in the 20th century.

Other conflicts listed, such as the Civil War and the War of 1812, occurred during earlier periods in American history, and while the Vietnam War did take place in the 1900s, it started in the mid-20th century and has different historical implications.