Who suggested that the south should secede from the union if an agreement could not be reached on slavery?

John C. Calhoun is the one who suggested that the south secedes from the union if an agreement could not be reached on slavery. 

He was a conspicuous U.S. statesman and representative for the slave-ranch arrangement of the prior to the war South. As a youthful congressman from South Carolina, he helped control the United States into war with Great Britain and built up the Second Bank of the United States. Calhoun went ahead to fill in as U.S. secretary of war, VP and quickly as secretary of state. As a long-term South Carolina congressperson, he restricted the Mexican-American War and the confirmation of California as a free state and was famous as the main voice for those looking to secure the foundation of subjugation.

Because broadest terms allows the law flexibility depending on changing society and circumstances.