> The military and national security state, plus the sheer amount of personal firearms, pretty much guarantees IMO that the US is basically impregnable from outside military interventions.

I find that a bit naive.

First, as for the point about firearms, I honestly don't think this is very relevant for the ability of a state to defend itself. Lots of firearms in civil possession might make life harder for domestic police - because they have (at least in theory) some obligation to protect the state's citizens and their property, even those citizens with firearms. So they cannot arbitrarily overpower those people.

An invading army has no such qualms. Just have a look at the wars that are currently going on, or the US' own invasions in the past. They have rockets, drones, airstrikes, artillery, tanks and all the other goodies at their disposal and will generally avoid getting anywhere near where your firearm could hit them. They won't try to arrest you, they'll simply blow up your house.

The second point has merit: The US not only has the most powerful national military in the world, it's also the leader of the most powerful international military alliance. Not to mention it is still at the center of the global trading and financial system, as well as the internet. Because of those factors, a chance of invasion is nil.

But that's nothing uniquely American, it just reflects the amount of power America currently has. Britain was in a similar position two centuries ago and Spain before that. It might change again.