Pfft, firstly russia doesn't hate us, and no fucking way would they risk that level of annihilation. UN are pussies through and through, and severely lacking in the men and equipment to mount any kind of mainland threat to the US. China has quite the manpower, but not the logistics to get it here. And make no mistake, it would take a land invasion, followed by a 3,000 mile wide guerrilla war against armed Americans, to pull something like that off.
Aint happening.