EMP is electromagnetic radiation from an explosion (especially a nuclear explosion). The worst of the pulse lasts for only a second but any unprotected electrical equipment - and anything connected to electrical cables, which act as giant lightning rods or antennas - are affected by it. If a nation with a nuclear bomb and the ability to explode it high above an American city were to do so, it would have a massive effect in all directions. Almost immediately all communications systems in the country would be disrupted completely. No radio. No television. No Internet. Indeed no electricity at all. Most of the country literally would be in the dark with no possibility of recovering any electrical facilities. We would not be able to run our cars because the gasoline pumps would not work. Water distribution systems would not work. While there would be few immediate deaths connected with such an explosion, the long-term consequences would be profound. The national power grid would be rendered completely impotent. It would take many months or even years to have it up and running but with no power tools available, accomplishing this likely would be impossible.

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