The economist had a pretty good article about that. It dealt with electromagnetic impulses, as those could take out several at once: http://www.economist.com/n

The economist had a pretty good article about that. It dealt with electromagnetic impulses, as those could take out several at once: http://www.economist.com/news/world-if/21724908-huge-potential-impact-rich-countries-prolonged-loss-electricity-disaster http://www.economist.com/news/world-if/21724908-huge-potenti...