Which of the following wars was fought by the United States in the 1800s?

The Civil War was indeed fought by the United States in the 1800s, specifically from 1861 to 1865. This pivotal conflict arose primarily over issues such as states' rights and slavery, leading to a divide between the Northern states (Union) and the Southern states (Confederacy). The war ultimately resulted in the preservation of the Union and significant changes in the nation’s laws and social structure, particularly with the abolition of slavery.

Understanding the context of the other wars helps clarify their timelines. World War I took place from 1914 to 1918, while the Korean War occurred from 1950 to 1953, and the Vietnam War took place from the late 1950s through 1975. These events occurred well after the Civil War, thus highlighting why they do not fit the question regarding wars fought in the 1800s.