I imagine most people here think that the USA is trying to conquer europe etc. Because most of the wars were happening in europe.
But lets assume that Europe is able to somewhat invade or at least bomb some of the US cities then you can be pretty sure that this would be devastating for the US moral. Noone ever was able to invade the US and (no offense) the superiority complex will somwhat kill the US from inside when they see that not only 2 skyscrapers are gone (like in 2001) but 95% of new york.
And since most of the big US cities are located "close" to the coast what else is left if San Francisco, NewYork City, Miami etc are gone? Sure there is tons of big cities but again think about the moral when those cities are gone.
I am not so sure N+S Dakota, Kansas, Nebraska, Iowa etc have alot of man power or have the needed importance to keep the moral high etc.
Other than territory Canada should not be a problem Ireland, Luxembourg, The netherlands and belgium combined should be able to win against Canada.
Mexico would be harder to conquer because of its population but since its not exactly the most advanced country in terms of weaponry it will still be alot easier to defeat than the US.
Since europe consists of a ton of countries most people in Germany France or Poland would not care if Madrid would be gone. But spanish people will fight like crazy to defend their capital city because its important for the countries moral etc.
