The major cause of civil war is slavery. In 1820, the Missouri Compromise divided the south and the north. The 36' 30" line was down to separate slave and non slave states in the territories. This division will lead to a lot of problems in the future.
In 1793, The cotton gin was invented. It is easier for people to pick up cotton. But it also increase the requirement of slaves. Because of that, when the north proposed to abolish slavery, it caused the dissatisfaction in the South.
The abolition of slavery will bring significant losses to the economy of the South. Therefore, John C. Calhoun put forward the idea of nullification: states could nullify or reject congressional acts they deemed unconstitutional.