I’ve never seen the Southampton Rebellion called a sectional issue before, unless by “sectional” you mean “Old Virginia vs. western Virginia.”
The underlying tension between the sections always had southern concern over the future of slavery as one component. As early as the first Congress under the current constitution, a South Carolina representative threatened on the House floor that his state would secede if Congress threatened slavery (in that case, by taxing slave imports). As Dew shows in his magisterial APOSTLES OF DISUNION, Deep-South secession commissioners’ appeal to the other southern states came down chiefly to “Secede with us, because Lincoln is a threat to slavery.”
Notice that no other state joined the Deep South in seceding in response to this call. Still, it was the Deep South’s call.
It is incorrect to say that slavery wasn’t the underlying reason for secession of the Deep South states. Without Virginia, however, the CSA could not have put up a four-year fight in defense of southern independence. Of course, it was Lincoln who decided on war.