The threat of an Electromagnetic Pulse (EMP) strike on this country is a very well documented one, I have written about the threat in the past and have used information from the EMP Commission report which was published in 2004 in several of my articles.  Most recently I read an article published over on the Economic Collapse Blog which sums up nicely what impact an EMP strike would have on our country.

via 7 actions to take immediately following an EMP strike : All Self-Sustained.