Some of the major causes of the Civil War were state rights and differences in the social and economical structure between the North and South. Slavery fit into all three of these categories and was another key component to the start of the Civil War.
Southern states wanted more power for individual states instead of a strong central, federal government. For example, the Missouri Compromise removed the ability of each state to decide whether or not it would permit slavery. As the country grew, southern states wanted to continue to expand slavery, but the Compromise prohibited this. Southern states also wanted the power to nullify federal laws, which was not granted.
Social and economic issues went hand in hand, as the northern states grew more industrial and urban while the southern states remained rural and based around plantations. As the north progressed, abolition became a common idea, and ideas about slavery grew more divided and controversial. With the election of President Abraham Lincoln, who was opposed to slavery, southern states had further reason to secede from the Union. Lincoln was elected without southern support, which created a further fissure between the two groups. The exclusion, differences and disagreements about rights and slavery caused the southern states to secede and form the Confederate States of America.