The original Red Dawn was memorable; not only was it a rah-rah patriotic cornball action movie, but it was a high concept film that even now still doesn't have much in the way of spiritual competition. "The Russians invade the United States" isn't exactly a common movie plotline--the only thing similar to it I remember crossing the screens in the last ten years is Tomorrow, When the War Began, with the plot of "countries that are TOTALLY NOT Indonesia and/or China invade Australia." Nevertheless, those two movies are reflective of certain national fears. Australia has historically had a rather uncomfortable relationship with its neighbors, being a large and thinly populated country surrounded by potential rivals overflowing with people. In 1984, when the original Red Dawn came out, the Cold War was heating up again after the 1970s détente. Ronald Reagan had called the Soviet Union an "evil empire" only a year before, and a significant chunk of the world was formally aligned against the democratic powers.
Red Dawn was hardly the only example of 1980s American invasion literature. There are plenty of lesser-known adventure stories and science fiction novels that depict America under the Soviet heel, enough that "post-cataclysmic rag-tag armies struggle to kick the Rooskies out of the good ol' US of A" is the very first entry in the Grand List of Overused Science Fiction Cliches. They were products of their time--sure, the Soviet Union was being pushed to the brink of collapse, but people didn't realize it at the time. The abrupt end of the Cold War in 1989 and the collapse of the Soviet Union two years later pulled the carpet out from under invasion literature quite neatly.
Now, though, times have changed. We're nervous again, especially in the United States. People have lost a lot of what they had and are afraid that they'll lose even more, and they're feeling compromised and vulnerable... in other words, people are in a receptive state of mind for invasion literature. How fortunate the new Red Dawn is there to come along. Here, have a trailer.
Lookit all those explosions of patriotism. Also a typo in the very first written thing we see. But I digress.
First off, keep in mind that the concept of Red Dawn is utterly ridiculous. Not only does it depict an invasion of the United States, which is hard enough to believe--the original movie began with a brief explanation of how NATO fractured and the United States became isolated just to help justify the premise--but it depicts an invasion of the United States by North Korea. Originally it was China, but there are the Chinese box office receipts to consider these days, and not many North Koreans go to the movies. The recent video game Homefront tried to do things this way too, making North Korea into a new evil empire by absorbing South Korea and Japan and bits of China and so on, but that didn't make it any less ridiculous. Just the opposite, in fact. The trailer implies that the invaders have some new weapon that enables them to turn off equipment, or something, but even something like that ignores the fact that a state like North Korea doesn't have the means to invade the United States even if it wanted to.
Logistics are important--an army without supply can't fight, and neither can it fight if you can't move it to where the war is. In the modern world of satellite surveillance and a dominant American military, the preparations to transport an army capable of putting a dent in the United States couldn't be overlooked. I suppose you could posit a world where things had changed, where the United States was isolated and unable or unwilling to respond until it was too late... except that world would not closely resemble our own. This is the sort of thing they did in the strategy game Red Alert 2, in which the United States remained quiescent as even Mexico joined the camp of its opponents... and even then, Red Alert 2 was a cornball strategy game with military dolphins and battle squid and combat zeppelins and psionic mind control and time machines built by Albert Einstein.
Because in this day and age, that's what it takes to invade the United States.
Works like Red Dawn are indeed telling; they illuminate aspects of the American psyche that aren't generally spoken about. They reveal America's fears. In Red Dawn, you don't see a country that spends five times more on its military than its closest competitor, and whose military budget is more than the rest of the top 15 countries put together. You see an idea of the United States of how it sees itself--a newcomer to the international stage, still convinced that everyone's gunning for it and trying to knock it off its perch. Maybe that's so. Still, attitudes like this reinforce uncomfortable memes. Spending $700 billion a year on defense isn't sustainable, not with the condition the US economy is in, but movies like this help to reinforce the notion that there are always enemies out there, and that the United States has to be armed to the teeth to keep them at bay.