What conflict took place from 1861 to 1865 in the United States?

The conflict that took place from 1861 to 1865 in the United States is known as the Civil War. This war was primarily fought over issues including states' rights and slavery, and it involved the Northern states (the Union) battling the Southern states that seceded from the Union to form the Confederacy. The Civil War was a pivotal event in American history, leading to significant social and legal changes, including the abolition of slavery through the 13th Amendment.

In contrast, the Revolutionary War occurred much earlier, from 1775 to 1783, when the American colonies fought for independence from British rule. The Mexican War, fought between 1846 and 1848, was a conflict over territorial expansion and the U.S. annexation of Texas. The War of 1812 occurred from 1812 to 1815, primarily involving maritime disputes between the United States and Great Britain. Thus, the Civil War is uniquely situated in the 1861-1865 timeline, making it the correct answer.