Name one war fought by the United States in the 1800s?

The Civil War is an important conflict in American history that took place from 1861 to 1865. This war was fought primarily over issues such as slavery and states' rights, and it was a pivotal moment that shaped the nation’s future. It involved the Northern states (the Union) fighting against the Southern states that seceded from the Union to form the Confederacy. The outcome of the Civil War had significant implications for the United States, leading to the abolition of slavery and laying the groundwork for civil rights advancements in subsequent years.

Other options refer to wars that either occurred outside the specified century or involved different historical contexts. For instance, the Revolutionary War was fought in the late 18th century, while World War I and World War II occurred in the 20th century, and the Korean War took place in the 1950s. Thus, the Civil War is indeed the correct choice for a war fought by the United States in the 1800s.