The main cause of the U.S. Civil War was the issue of slavery, particularly its expansion into newly acquired territories and states. The conflict arose primarily between the Northern states, which were largely anti-slavery, and the Southern states that were committed to maintaining and expanding the institution, which they viewed as essential to their agrarian economy. Tensions escalated due to political compromises, the Dred Scott decision, and the election of Abraham Lincoln, who opposed the spread of slavery. The war officially began in 1861 following the secession of several Southern states, ultimately leading to a bloody conflict over the nation's moral and economic foundations.