North Korea and Iran don’t have NEARLY the capability to launch an EMP Strike against the US. F-14s and Mig 17s from 1/2-3/4 of a century ago are not going to get through NORAD, or even get close enough to the US to be under the jurisdiction of NORAD. Honestly, I don’t know that China has capability to deliver an EMP to the US either. The US has not prepared for a domestic war against those countries, it has prepared for “if they get annoying enough, what’s the easiest way to invade and destroy them”.
A single EMP strike would not take out the entire country. US domestic nuclear launch facilities are hardened against EMPs, as is a large area underneath the Pentagon, Air Force 1, The White House, and many other command and control locations, not to mention the multiple nuclear-capable carrier strike groups we have at sea pretty much constantly since the aircraft carrier was invented. While we can’t know for sure, it is INCREDIBLY likely that there is some sort of protocol for nuclear subs to launch if they don’t hear anything from their commanders after a certain amount of time. Not to mention US forces and diplomats all across the world, as well as the aforementioned EMP-hardened parts of the US military command and control. As I said before, I don’t know where you are getting your info, but I suggest not following that source and taking a chill pill.