Which war was NOT fought by the United States in the 1800s?

The United States did not fight in World War I during the 1800s; this conflict took place from 1914 to 1918. The other wars mentioned occurred in the 19th century. The Civil War occurred from 1861 to 1865, the Mexican War was fought from 1846 to 1848, and the Spanish-American War took place in 1898. Therefore, identifying World War I as the war not fought by the United States in the 1800s is accurate. This distinction is critical for understanding the historical context of U.S. military involvement and the timeline of major conflicts.