Alien invasion is a form of Science Fiction that primarily revolves around the theme of aliens invading the Earth (or Earth-like planets) and other human habitations, typically for hostile motives, though benevolent alien intervention has also been present in the genre's history. Having its origins in early sci-fi literature like H.G. Wells' seminal work The War of the Worlds, the portrayal of alien invasions (in addition other alien-human interactions) has become a common sci-fi theme in the 21st century.
The genre's popularity has given way to plenty of different styles based on the theme, from aliens inflitrating societies as human clones, Horror films and Thrillers revolving around encounters with deadly, horrifying aliens, to large-scale War plots, and more subdued, philosophical films attempting to discuss the thought-provoking matters reagrding alien and human relations.
