Which two wars were fought by the United States in the 1800s?

The Civil War and the Mexican-American War are both significant conflicts in U.S. history that occurred during the 1800s. The Civil War took place from 1861 to 1865 and was primarily fought over issues like slavery and states' rights. It resulted in substantial changes to the United States, including the preservation of the Union and the abolition of slavery.

The Mexican-American War was fought between 1846 and 1848 and stemmed from territorial disputes following the U.S. annexation of Texas. This conflict resulted in significant territorial gains for the United States, including present-day California, Arizona, New Mexico, and parts of Colorado, Utah, and Nevada.

The other options refer to conflicts that occurred either before or after the 1800s. The Revolutionary War occurred in the late 18th century, and both the Vietnam War and the Korean War took place in the 20th century. Lastly, World War I occurred from 1914 to 1918 and the Gulf War occurred in the 1990s, both of which fall outside the 19th century. Thus, the correct pairing of wars from the 1800s is indeed the Civil War and the Mexican-American War.