You're forgetting about the massive economic crash that would occur, the resulting worldwide depression, and inevitable shortages of everything from grain (which now can't be harvested) to oil, medicine, and toys. Millions would be unemployed from this, or be facing unemployment, in just the US alone. Without the US' production, food and other supplies in places like Somalia, Mexico, and elsewhere fall sharply and soon famines and civil wars break out in those regions. The world's remaining powers would be forced to intervene, but keeping both North America and the 3rd world afloat would be too much, and it would take awhile for things to get back to normal. Global technological advances are severely crippled by the loss of the likes of Silicon Valley and New York.

Needless to say America is knocked off our pedestal, and likely China takes its spot as the leading world power. Without American influence, Russia's dominance in Europe grows and we could see some countries in the EU/NATO break away to join Russia's orbit.