Which event did not occur in the 1800s?

The Spanish-American War is an event that took place in 1898, and the Civil War occurred from 1861 to 1865. The Mexican-American War lasted from 1846 to 1848, making these three choices events that indeed happened during the 1800s.

In contrast, World War I began in 1914 and lasted until 1918, which places it in the early 20th century, well outside the 1800s timeframe. This differentiation in the historical timeline makes it clear why World War I is not associated with the 19th century. Understanding the specific years that these conflicts took place is essential for context and illustrates the timeline of U.S. history in relation to international events.