Gary, as you AND we all have stated many times the threats are/can be varied and many. They CAN consist of:

1. Global Thermal Nuclear War (think about the Movie War Games).
2. EMP (Electrical Magnetic Pulse) (Hi altitude nuclear Explosion frying integrated circuits so that virtually NOTHING will work.
3. An Attack on our electrical infrastructure
4. An attack on our fuel, coal, gasoline, Natural Gas, along with wind and solar production facilities and distribution systems.
5. An attack on our food distribution system.
6. Mass simultaneous terrorist acts.
7. An attack on our Rail (Train) system

I am sure there are others but these come to mind. a disruption to any one SINGLE of these "Systems" would lead many people into mass panic mode, reverting to the Rule of the jungle where only the strongest survive.

Who's next?