I beleive both northeners and southeners believe that the secession would lead to war
The main reasons for conflicts regarding secession is not economic reason like the southern states said. But it's matter of principles.
It's a matter of whether we can enslave other human beings and treated them as object. The northern states held this principles that slavery should never happen. When the south decided to seceed, it's a matter of time before the northern states would come with their armies.