The 1st book starts after the collapse and after a depopulating pandemic that came after the collapse. What set the collapse itself in motion was an ill-fated Mideast war that results in a couple nukes going off in American cities which then sets in motion a downward cascade of economic and infrastructure failures. The isolation of Union Grove is such that we know nothing of what is happening elsewhere in the country or the world until the 3rd book. We then learn that as we might expect, post collapse conditions are not uniform given cultural, religious, geographic,and climate differences in a country as large as the US.
Kunstler, like every other writer in this genre, ignores the elephant in the room……. the nuclear power plants and what happens to them after the grid fails. I otherwise find Union Grove and its inhabitants believable, but as I said in my 1st post, the setting is just a few miles from Vermont and is culturally recognizable to me.