The South ran it alone against an industrialized North. They were doomed to failure unless they had foreign alliances active in the war.
Did they really think that the secession would result in war; that a their brothers to the North would attack them? From what I’ve read in the past, some believed that they would secede and that would be that. They had threats from the Union, but dismissed them as saber rattling.
IIRC, they began raising armies immediately, on the supposition that secession would result in an invasion by the North.