a) some northern states were refusing to follow the fugitive slave act.
b) the federal government was poking it's nose into the slavery question, and the south didn't think it belonged there.
c) The president elect was anti-slavery.
In short, the south backed an economic strategy which limited it's political clout and when whining about it stopped working they started a war.
Their idea of an offer you can't refuse is an offer... and you'd better not refuse.