I still think the coolest thing about the original Red Dawn was the theme music.
If I remember High School Physics correctly, if you detonate a nuclear warhead in the one highest levels of the atmosphere either the mesosphere or stratosphere, the energy from the blast creates an Electro Magnetic Pulse which would wipe out electrical grids. The benefit is that the blast does not have the destructive force of a low level detonation that basically destroys everything and makes the area unhabitable for a couple hundred years.