In the first few minutes of an EMP, nearly half a million people would die. That’s the worst-case scenario that author William R. Forstchen estimated in 2011 would be the result of an EMP on the electric grid — whether by an act of God, or a nuclear missile detonating in Earth’s upper atmosphere.
An electromagnetic pulse is a burst of electromagnetic energy strong enough to disable, and even destroy, nearby electronic devices.
The scenario sounds like something in a Hollywood film, but the U.S. military has been preparing its electronic systems for such an event since the Cold War. The protective measures taken to harden facilities against a nuclear attack also help in some cases to protect against EMPs.
The civilian world is another story.