It's one in a set of USA wet-dreams and it's quite common because, to a very large amount of people (including people of other nations), it's a highly intriguing premise. Imagine, one of the most powerful nations in the world faces off in an apocalyptic war against another equally powerful nation. Obviously the US of A is the best candidate for this even for foreign audiences as it's an extremely well known country. Very few other countries can match, at least in the western world. It's not uncommon that people of other nations know more about USA than they know about where they themselves come from.
What I am truly tired off from all these depictions of this "final war", is that the bad guys are virtually always the same, and rarely if ever is any proper reason for the attack ever given. It tends to boil down to the old "because we hate your freedom and decadent lifestyles, capitalist pig!", and that I believe were all over and done with.
Of course, if a movie, game or book wanted to depict a realistic scenario, they would never chose an invasion of mainland USA, it's simply too unlikely... I hate to say it, but there is no country in the world currently with invested interest in performing an all-out attack on the US, at least not a country that has such capabilities remotely available...
