Some guy who calculates the chance of a flood wiping out your house has also
calculated some other numbers you might be interested in.
Stepping through this, the average year for colony establishment is 1678, which is 340 years ago. Two qualifying events in 340 years is a 0.5882% annual chance of nationwide violent revolution against the ruling government. Do the same math as we did above with the floodplains, in precisely the same way, and we see a 37% chance that any American of average life expectancy will experience at least one nationwide violent revolution.
This is a bigger chance than your floodplain-bound home getting flooded out during your mortgage.
Buy more ammo. And another gun, if you can.