The alien invasion is a common theme in science fiction

Science fiction

Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 stories and film

Science fiction film

Science fiction film is a film genre that uses science fiction: speculative, science-based depictions of phenomena that are not necessarily accepted by mainstream science, such as extraterrestrial life forms, alien worlds, extrasensory perception, and time travel, often along with futuristic...

, in which extraterrestrial

Extraterrestrial life

Extraterrestrial life is defined as life that does not originate from Earth...

 life invades Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 either to exterminate and supplant human life, enslave it under a colonial

Colonialism

Colonialism is the establishment, maintenance, acquisition and expansion of colonies in one territory by people from another territory. It is a process whereby the metropole claims sovereignty over the colony and the social structure, government, and economics of the colony are changed by...

 system, harvest humans for food, steal the planet's resources, or destroy the planet altogether.

The invasion

Invasion

An invasion is a military offensive consisting of all, or large parts of the armed forces of one geopolitical entity aggressively entering territory controlled by another such entity, generally with the objective of either conquering, liberating or re-establishing control or authority over a...

 scenario has been used as an allegory

Allegory

Allegory is a demonstrative form of representation explaining meaning other than the words that are spoken. Allegory communicates its message by means of symbolic figures, actions or symbolic representation...

 for a protest against military hegemony

Hegemony

Hegemony is an indirect form of imperial dominance in which the hegemon rules sub-ordinate states by the implied means of power rather than direct military force. In Ancient Greece , hegemony denoted the politico–military dominance of a city-state over other city-states...

 and the societal ills of the time.