"Looking back on the appalling 21st century from our vantage point, 500 years later, it sometimes seems incredible that the human race could have survived such a time of troubles. The moment of greatest danger can now be pinpointed precisely--the year 2010.
Fifty years earlier, the chief threat seemed to be from thermonuclear weapons; however, these could be manufactured only by wealthy nations possessing both vast financial resources and a high level of technology.
Then, suddenly and totally unexpectedly, the situation was transformed by the invention of the Electromagnetic Pulse Bomb. The origin of this terrifying device is unknown: Like most concepts whose time has come, it was probably invented independently in a number of places. However, the first public account appeared in the September 2001 issue of Popular Mechanics under this dramatic headline:
E-BOMB: In the blink of an eye, electromagnetic bombs could throw civilization back 200 years. And terrorists can build them for $400." (more)
Hummm... Time to buy a horses and a farm next to a river. You'll need the land for crops, horses for transportation and cultivation and water for power.