The major cause of the American Civil War, according to numerous historians, was the issue of slavery and its expansion into new territories. The conflict arose from deep-seated tensions between the Northern states, which were largely anti-slavery, and the Southern states, which relied heavily on slave labor for their agrarian economy. Debates over states' rights and economic differences further fueled the conflict. Ultimately, the election of Abraham Lincoln in 1860, who opposed the expansion of slavery, escalated tensions and led to the Southern states' secession and the outbreak of war.