If something were to happen, I am not sure that future historians would call it a “civil war”.
More likely, if anything was to shape up, it would roughly be described as urban versus rural.
Shortages of significant impact would draw people out from the densely packed urban areas so that they could ransack small town America.
From a bit of the stuff I’ve seen, though, if there were major civil disturbances, one of the first things that would happen is important assets like oil refineries would be secured, and all travel into/away from large metropolitan areas would be stopped.