To provide some context for my question, societal collapse (of America in particular) was due to a combination of war, infected creatures, and additional destruction by civilians. Let's say much of the infrastructure was destroyed, too few people survived to restore/maintain cities, and the few people who survived in bunkers/arcologies/etc haven't yet reclaimed their surroundings:
Would the less fortunate survivors become tribal (e.g chiefdoms, nomadic, etc) within a decade or two, given America's size and arduous landscapes?
I'm not imagining an equivalency to tribes of a pre-industrial world as I suspect some modern knowledge, technology, and norms would persist and be implemented accordingly, nor am I intending for every group to be tribal; a few groups have established neo-feudal societies.
Environmental factors have also been considered. I suspect people on the eastern U.S. (especially the southeast) would be more vulnerable to natural disasters without advanced warning systems, thereby burdening their recovery and hastening the decay of infrastructure; that agriculture in the southwest (and comparable areas) would be greatly scaled down without advanced irrigation, presumably encouraging more nomadic lifestyles and conflicts; and that hunting and conflicts would be more present in regions with short growing seasons and cold winters.
I've also considered the impact of (additional) carnivores that escaped zoos though I'm skeptical if they could propagate fast enough to be anything other than exotic meals briefly present on the continent; the infected are the main non-human threat.
Do correct any underlying misconceptions, and apologies for the American bias in the inquiry; some survivors are stranded tourists though :)/:(. Any understanding of your comparable biomes is welcomed.