The Upper South Secedes … well, some of it

Explanations of secession often obscure the fact that of the fifteen slave states in 1860, eight had not seceded at the time of Fort Sumter.  Even after the firing on Fort Sumter, four slave states still remained within the Union, although three were divided (and I think Kentucky’s “neutrality” is in its way a form of conditional unionism that comes close to secession, and that’s being kind).  Only Delaware seemed fairly safe: in Maryland and Missouri rival sides continued to class, just as in Tennessee and Virginia there remained significant pro-Union elements.

What I find interesting about scholarship covering the secession crisis is that most of it concerns the decision-making of the Lincoln administration.  Yes, there are some very nice studies of politics in the upper South (Dan Crofts’s Reluctant Confederates takes pride of place in my mind), but we don’t have much of a Confederate counterpart that talks about how Jefferson Davis chose confrontation and risked war.

That said, and setting aside the role of slavery in the secession of the Deep South, how do you explain the secession of the Upper South?  What role does slavery as an issue play in that decision?  What role does what happened at Fort Sumter trigger secession?