Alien invasion
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This article is about invasion by extra-terrestrial beings as a theme; for other uses of the term, see Alien invasion (disambiguation).
The alien invasion is a common theme in science fiction stories and film, in which an extraterrestrial society invades Earth with the intent to replace human life, enslave it under a colonial system, or in some cases to use humans as food.
The invasion scenario has been used as an allegory for a protest against military hegemony and the societal ills of the time. Wells' The War of the Worlds is often viewed as an indictment of European colonialism and its "gunboat diplomacy" setting a common theme for some politically motivated future alien invasion stories.
Prospects of invasion tended to vary with the state of current affairs, and current perceptions of threat. Alien invasion was a common metaphor in US science fiction during the Cold War, illustrating the fears of foreign (i.e. Soviet Union) occupation and nuclear devastation of the American people. Examples of these stories include "The Liberation of Earth" by William Tenn and The Body Snatchers.
In the invasion trope fictional aliens contacting Earth tend to either observe (sometimes using experiments) or invade (Plan 9 from Outer Space, and the Daleks and others in the long-running series Doctor Who), rather than help the population of Earth acquire the capacity to participate in interplanetary affairs. There have been a few exceptions, such as the alien-initiated first contact that begins the 1951 film The Day the Earth Stood Still, and the Vulcan-initiated first contact that concludes the 1996 film Star Trek: First Contact (although after a failed invasion by the Borg in the rest of the film). In both cases, aliens decide to visit Earth only after noticing that its inhabitants have reached some threshold level of technology: nuclear weapons combined with space travel in the first case, and faster-than-light travel using warp drive technology in the second.
As well as being a sub-genre of science fiction, these kind of books can be considered a sub-genre of Invasion literature, which also includes fictional depictions of humans invaded by other humans (for example, a fictional invasion of England by a hostile France strongly influenced Wells' depiction of a Martian invasion).
