An Economical Collapse is more likely, second is an EMP attack. The two are on the top of my list.
Economical or Financial Collapse: The National debt is out of control and when/if the interest rate start going up there is no way that we can pay the interest on the National debt. $17.5 Trillion http://www.usdebtclock.org/ and we are paying what interest right now? Wait till it goes up just 1%, it’s unsustainable! The numbers don’t add up, numbers do not lie.
EMP: North Korea, Iran, China, Russia, Al Qaeda and maybe one or two others that I may have left out, all want us dead and EMP is the best and cheapest way to do it. For China and Russia it also means they didn’t have to destroy the valuable assets in the U.S. just kill the population.