The primary cause for the secession of Southern states from the Union was the contentious issue of slavery. Southern states believed their economy was heavily reliant on slavery, particularly for their agricultural sector, and they viewed any threat to this institution as a direct threat to their rights and way of life. The election of Abraham Lincoln in 1860, who opposed the expansion of slavery into new territories, intensified these fears. Consequently, in 1861, eleven Southern states seceded from the Union, leading to the Civil War as they sought to establish their own nation, the Confederate States of America.