One High-Altitude Electromagnetic Pulse Can Shut Down and Make Inhabitable Much of the US
Steven Starr, a scientist at the University of Missouri, has made available his analysis of the effects on US infrastructure, communications, and nuclear power plants from the explosion of a nuclear weapon 42 miles above the US. As the US has not shielded against electromagnetic pulse, the effect would be catastrophic.
https://nuclearfamine.org/connect/