You didn’t mention the failure that would cause the end of the world as we know it most quickly: the internet.
Without the internet, the EBT system goes down and after the ferals rob and loot all the food out of the grocery stores in a few days, they will take it from whoever has it. You preppers think you’re ahead of the game but tell you what, you can’t resist a hungry mob that outnumbers you a hundred-fold or more.
Our enemies know this, and the only thing that stops them is it would result in such a mess to clean up no one dares use an EMP weapon. Killing the internet is the new neutron bomb - it would wipe out all human life in short order and no amount of preparation or buried caches of books will stop it.
FReepmail me for details.