Alien Invasion is self-explanatory and the target is usually, but not always, our Earth. It is a common theme in science fiction stories and film, in which extraterrestrials invade Earth either to exterminate and supplant human life. The classic of this subgenre is H.G. Well's War of the Worlds, which has been presented in radio by Orson Welles' in 1938, the 1951 feature film classic, and Stephen Spielberg's film version.The film Independence Day, by Roland Emmerich, has become a cultural milestone.
I didn't include films where there is an encounter or conflict involving a single alien entity such as Predator or John Carpenter's The Thing, those type of alien encounter films are highlighted in our Extraterrestrial Sci-Fi section. Other films such as Oblivion, which employs both post-apocalyptic and alien invasion, are really a toss up where they are sorted. So in films like Oblivion, it's featured in both SFMZ's Alien Invasion and Post-Apocalyptic sections. Other invasion films where infiltration is the alien's agenda via subterfuge are also included, such as The Arrival or Invasion of the Body Snatchers.
The fifties Alien Invasion films listed below are featured in SFMZ's Fifties Sci-Fi section.