Answer:
Prior to the war, the North and the South had been divided for decades over the issue of slavery. Measures such as the Missouri Compromise and the Compromise of 1850 had failed to settle the issue.
The Southern economy was based largely on plantation agriculture, and African American slaves did most of the work on the plantations. The Northern economy, on the other hand, relied more on manufacturing. By the 1850s abolitionism was growing in the North, causing the Southern states to fear that the federal government would attempt to end slavery.
The Southern states believed that the U.S. government did not have the right to decide whether slavery should be allowed in a state.