Which of the following wars was not fought by the United States in the 1800s?

The correct answer is the choice that identifies World War I as the conflict not fought by the United States in the 1800s. World War I occurred later, from 1914 to 1918, with the United States entering the war in 1917.

In contrast, the Mexican-American War took place between 1846 and 1848, the Civil War was fought from 1861 to 1865, and the Spanish-American War occurred in 1898. All of these wars were significant conflicts for the United States during the 19th century, involving military engagement and substantial political and territorial implications. Understanding the timelines of these conflicts highlights the distinction of World War I as an event solely in the 20th century.