What did Calhoun threaten if the north did not agree to the demands of the south?

John C. Calhoun threatened that if the North did not agree to the demands of the South, particularly regarding the protection of slavery and states' rights, the Southern states might consider secession from the Union. He argued that the South had the right to protect its interests and warned that failure to address their grievances could lead to a breakdown of the Union. Calhoun's position emphasized the growing tensions between the North and South that ultimately contributed to the Civil War.