If the rest of the world turned against the USA, the USA would be fucked.
http://www.nationmaster.com/graph-T/mil_wea_hol
http://www.nationmaster.com/graph-T/mil_arm_for_per
http://www.nationmaster.com/graph-T/...va_mal_age_154
IMHO China could take us if Europe didn't assist us. They have almost as much weaponry, with twice the armed forces, and three times the available manpower; growing rapidly every year. Throw in N.Korea and we don't stand a chance.
EU + Russia could fuck us up too. But that's less politically likely.
Of course, nukes
still gaurantee Mutually Assured Destruction.