If they do pull a surprise attack, the us would pull there troops and send them to the country that is doing this attack. The US still has tons of troops in the US and tons of weapons, planes and ships. + other countries would be there to help. Austraila would come out and help full force, and I am pretty certain if the US was in that trouble Canada would step in. Canada has already mentioned they are going to help rebuild Iraq.
I do believe North Korea will be joining this war very soon.
-Sam.