Originally posted by: C3PX
I was talking about a Nuclear detonation in the atmosphere causing an EMP. That would knock out a lot more than a few square miles.

Actually, it may not knock out anything at all. Watch "Trinity and Beyond: The Atomic Bomb Movie". They show several atmospheric bomb tests and all that happens is the lights dim and the radio gets crackly. I don't know the size of the bombs that were detonated, but they were close enough for the soldiers to see the blast and for the EMP to cause that. A big one may be able to knock out a lot of power, but you'll have a lot more to worry about than EMP if there's a nuclear detonation in the atmosphere. You'll be dealing with fallout and a massive loss of life as well.