Another take on things...
All of those criticizing the premise behind both the original “Red Dawn” and this remake are assuming that the geopolitical landscape we have today (or 30 years ago, in the case of the original movie) is the same in the movie’s “universe”. The original was released in 1984, but they don’t ever tell you if the story takes place in 1984, or sometime in the not-to-distant future. In this earlier version, Russia invades through Mexico, if memory serves me, and made use of Cuban (or some Central American nation’s or nations’) troops for occupation duty, backed by Soviet logistics. They imply that Russian troops are also involved, probably at the front, but the USSR is also fighting China, who comes into the war on our side (or at least are co-belligerents). So the geopolitical situation in the film was very likely different from the reality of the time it was released.
The movie also implies that D.C. was hit in some sort of surprise, but limited nuclear attack. A large majority of our forces are (were) stationed in Europe, and the film also states that NATO basically surrenders when the USSR threatens them with a nuclear strike, hanging the cream of our conventional combat forces out to dry. With both sides still holding enough nuclear forces to decimate the other, the initial success of the invasion is replaced by a war of attrition sets. Perhaps like Japan in the Second World War, the Soviets hoped the will to resist would be quickly broken by the decapitation strike against our military and political leadership, and the rapid occupation and pacification of a significant portion of CONUS.
Now let’s turn to this modern version. I have only seen the trailer, so I’m going to have to make a few assumptions. The year is 2021. Let’s assume that the United States, after numerous and costly wars in the middle-east, finally says enough is enough. We’ve managed to overcome the political opposition to utilizing our own vast reserves of fossil fuels, as well as our fear of nuclear energy, and achieved energy independence. With anti-military isolationist in power in the US, we’ve essentially abandoned the world stage, pulling out of all military alliances, pulling all forward deployed forces home, and decommissioning a large percentage of our military; China steps in to fill the vacuum.
A currency and trade war brews between China and the US. The Chinese move to replace the US dollar as the world’s reserve currency with China’s currency. This trashes the US economy and, finding itself suddenly isolated and without allies, the US retaliates by defaulting on the huge national debt (a significant percentage is held by...wait for it...China). Thinking the US is now just a paper tiger with no national will to resist, China builds up military forces in Central and South America, as well as in Cuba (they are Cuba’s new best buddy, having helped them develop oil production in the Gulf, during those years that anti-fossil fuel extremists were in power in Washington).
From here, the pattern follows the first Red Dawn movie: a limited nuclear strike, followed up by an invasion by land (again, through Mexico), sea (having spent decades building a blue-water navy), and air. The front-line troops are Chinese regulars, but they make use of Korean troops (North Korea having rolled over South Korea after the US pulled out) to seize and occupy certain strategic crossroads (one in Colorado, as it happens). Half the country is occupied, but the war stalemates; the USA manages to hold onto about two-thirds of its territory, and China (while extremely powerful) lacks the logistical skill to press the attack and achieve a decisive breakout. A resistance is quick to form in the occupied territories, to disrupt the occupation...
Least that's one way it could go. I'm not saying it's a likely scenario, but it's not totally outside the realm of the possible.
