Answer:
the U.S. government refused to recognize the southern states’ right to secede from the Union, and the C.S. government asserted that right by seizing federal property within its states' borders.
Explanation:
Although the Historians mostly believe that it is not one of the main causes of the war (it was most likely a proponent, only), this is what the supporters of the idea of State's rights commonly argue as the main reason for the Civil War.
