What was one war fought by the United States in the 1800s?

The Civil War was a significant conflict in the United States that occurred from 1861 to 1865. It primarily arose from tensions surrounding issues such as slavery, states' rights, and economic disagreements between the Northern and Southern states. The war ultimately led to the preservation of the Union and significant changes in American society, including the abolition of slavery through the 13th Amendment. This conflict played a critical role in shaping the future of the United States and its governance.

Other wars mentioned occurred outside the 1800s, like the Revolutionary War, which was fought prior to that century, and the Spanish-American War, which took place in 1898. The War of 1812 is also a correct choice as it occurred just at the beginning of the 19th century, but the Civil War is a more impactful and well-known conflict directly tied to the societal changes of the latter half of the 1800s.