EMP or electromagnetic pulse is the byproduct of a nuclear reaction. Electromagnetic fields passing through conductors at a generating station is what produces current flow in everything that uses electrical power. TV’s computers, water pumping stations, lights, refrigerators, cars, radios, nowadays just about everything. If the field is strong enough, the current flow through the conductor will cause it to disintegrate. Integrated circuits (computer chips) are particularly suceptable to high current flow. A nuclear blast, hundreds of miles above the surface of the earth, would project the EMP radially in all directions line of sight to the earths surface rendering all communication, transportation, power grids, generating systems useless for a very long time. No one would die from the blast, but millions would die from starvation, thirst and the chaos that follows. A container vessel off the east coast could feasibly launch a missile, no advanced guidance system required, into the atmosphere 300 miles up, detonate it, and the entire east coast as far west as Ohio, would be knocked back 200 years. Your faucet would dry up, Trucks wouldn't run to bring food to the grocery stores, police cars wouldn't run, your lights wouldn't turn on, zippo zilch on everything relying on a computer chip would stop working. And that's just about everything. Buy a gun, because if this ever happens, you're gonna need one.