The entire premise of all the states duking it out against each other ( imagine MO trying to win anything on an 8 state front?).
If anthing occurs regarding total breakdown of fedgov influence, regions that have interstate ties and mutual aid/benefit capabilities would band together. TX, LA, MS AL FL all have ports, Upper MW and MW has resoures and lines of communications t the Southern regions, oil, NG raw materials, manufacturing etc all enabled by the big rivers, but also bounded by natural obstacles like the Rockies and desert SW, Mississippi R & Appalachian’s to the east, cold zone to the north. West coast has much of the same, east coast too. Cities would be the toads n the roads, feral populations who cannot produce much internally, food, shortages etc. farmers markets, hunting fishing are the local rural personal resource, wood, water in abundance. close in rural areas would be predated for some time while fuel remained, but rural folks shoot first, shovel second. It would not take long for rural defense forces to form, and begin road blocking.
Example- 12 of 14 neighbors with a two mile radius of me are retired veterans, all hunt fish ranch or farm and can cover one anther with fires from the porch in most cases. A all wx creek runs through the valley, lots of forest but clear field so fire, only two roads transect the local valley, we know one anther and have similar cultural backgrounds. I think we’d do okay. One diesel shop, a veterinarian, a MD, a NP, engineer, welding shop, one guy has a 100 kw generator ready to plug into the grid and 5000 g of diesel ( the mechanic) says we would run it two hours a day for 6 months for water pumping/necessities etc. Over 150 cattle on the pastures, everyone grows fruit and veggies and cans. We all have generators chainsaws and (some of us have) decent amounts of gasoline on hand. Since jobs would go, we all would have time on hand to watch and cover while we tend to truck production and such. I doubt the Sherriff would be trying to evict us either once we all defaulted on mortgages.
Replicate that scenario times a million or two rural enclaves. Compare to the city folks.... they’d be starving in a week, out of water in a month or less (most get water from rural areas, and that requires a presence and power to pump) and fighting each other for scraps...
Once fuel ran out, we would be accustomed to less anyway, so we would do fine.
you’ve kind of skipped over the immense manpower advantage - even diluted by their infighting and sedentary lifestyles - that cities have.