When did we go from 'self-sustaining' to societal collapse? It seems to be some weird fantasy where these isolated towns are somehow more self-sustaining becaus

When did we go from 'self-sustaining' to societal collapse? It seems to be some weird fantasy where these isolated towns are somehow more self-sustaining because they could vaguely survive in the case of a societal collapse. That doesn't make them self-sustaining in modern society. And saying that roads are a luxury seems to be incredibly ignorant of how society evolved and how important trade routes (as well as ocean access, something cities generally have) for getting resources you otherwise don't have access to. Such as materials, spices and meds. Something that, you know, an isolated farm wouldn't readily have access to. Especially since salt is kind of a big deal for food preservation.