Which war was fought between the North and South regions in the United States?

The war fought between the North and South regions in the United States is known as the Civil War. This conflict occurred from 1861 to 1865 and was primarily a result of long-standing tensions over issues such as states' rights and slavery. The North, known as the Union, opposed the expansion of slavery, while the South, or the Confederacy, sought to maintain and expand slave-holding territories. The Civil War was a significant moment in U.S. history, leading to the preservation of the Union and the eventual abolition of slavery. Understanding this context highlights why this option is the most relevant to the question. The other wars mentioned—such as the Revolutionary War, World War I, and the War of 1812—were fought over different issues and involved different regions and nations, not specifically the North and South of the United States.