The immediate cause of the U.S. Civil War, which began in 1861, was the election of Abraham Lincoln as president in 1860. Lincoln's anti-slavery platform and his commitment to halting the expansion of slavery into new territories alarmed Southern states, which relied heavily on slave labor for their agrarian economy. Fearing that their way of life was under threat, several Southern states seceded from the Union, leading to the formation of the Confederate States of America. This culmination of tensions over slavery, states' rights, and economic issues ultimately ignited the conflict that became the Civil War.