Okay first post and highly fictional assumptions but here’s my opinion...
High Altitude Super EMP weapon... perhaps onboard a routine satellite which suddenly fails (Russian, Chinese etc) and falls out of orbit and detonates
20-40 km above the Northern United States.
That wouldn't clear the way for a conventional land invasion but would certainly cause a lot of technical damage.
The next bit is also highly improbable and sounds like something from '24' but is not impossible…
If said unfriendly nation also had operatives on the inside of the United States (either their own or duping right wing extremists to do their dirty
work) couple the above with targeted non nuclear EMP (NNEMP) devices at strategic pressure points e.g. Cheyenne Mountain Operations Centre (NNEMP
payload could be delivered by drones, cruise missiles (perhaps fired from a cargo freighter off the coast) or even hand/body held devices.
All this is a bit of a stretch and more of a fiction novel, but if an unfriendly nation could pull the above two scenarios off within a pretty
synchronised time span, the USA's technical defences would be temporarily removed or severely damaged and perhaps limiting the US’s ability to
respond with nuclear strikes (though the USA would still have plenty of submarines out at sea with viable payloads).
Given that the High Altitude Super EMP would probably have also disrupted most satellites in its vicinity communications would also be disrupted which
could cause a problem with communicating with any such sub (but who knows what automatic protocols exist should such an attack ever happen).
The aggressor country would probably then have a short timescale to launch an attack based on conventional weaponry - cruise missiles, ballistic
missiles, tactical nuclear missiles at high value targets. I imagine the rest of NATO at this point would be swiftly reacting and giving the USA
access to all the satellite tracking and electronic data from the other side of the sphere that would still be working as one attack on a NATO member
is an attack on all.
If in the timescale above the aggressor country managed to take out suitable high value targets and reduce the power of the United States defences it
would leave the US with many technical problems but still no land based invasion.
So even though a lot of damage could be done to the mainland USA I just can't see anyone being able to land a conventional army on the United States
shores anytime soon. Even in the above scenario if said aggressor nation somehow managed to get to the United States either on beaches or through
Canada or Mexico they'd face massive resistance from home-grown conventional troops and weaponry that survived the EMP.
The only way to launch a convential attack on the USA would be to take out the rest of NATO first as the said aggressor nation would probably be
shortly wiped from the face of the map by NATO. My imagination isn't good enough to even come up with a fictional scenario of how anyone could take
out NATO itself unless either the US, France, GB or Germany went rogue.
So a lot of damage could be done to the United States but no land based invasion (this is not taking into account classified technology that I have no
idea about). Remember the above scenarios are fictional and would take a hell of a lot of coordination and luck to even have a cat in hells chance of
A good article on EMPs and Super EMPs can be found here www.futurescience.com...