What led many of the southern states leave to the union?

Many Southern states left the Union primarily due to disputes over slavery and states' rights. The election of Abraham Lincoln in 1860, who opposed the expansion of slavery into new territories, heightened fears among Southerners that their way of life and economic interests were under threat. This tension culminated in the belief that secession was necessary to preserve their rights and maintain their social order. Consequently, several states seceded, leading to the formation of the Confederate States of America and the onset of the Civil War.