It functions more as a speculative documentary examining the possibility of an invasion of the United States by a formidable, organized, and intelligent opposing force than it does as a straightforward action film. The invaders could plausibly be from Russia or Germany—they definitely aren’t aliens. A significant portion seems to consist of existing footage; while this isn't inherently negative, as it can provide a sense of realism regarding warfare, particularly aerial sequences, the way it’s employed doesn't quite hold up under close examination – historical events appear misplaced geographically. Despite that, there are still plenty of enthusiastic lines and patriotic presidential speeches, stirring calls to action, and news reports that leave you feeling confident in America’s ability to overcome the invasion. It isn’t terrible, nor is it overtly an anti-Soviet piece of promotion, but the performances feel unimportant and the underlying purpose is obvious: “America, get ready.”

Source on TMDB