Notable examples

The classic treatment was The War of the Worlds by H. G. Wells, which was made into movies in 1953 and 2005, as well a numerous Radio adaptations and a TV series. Another early version is The Germ Growers (1892), by Robert Potter.

Other treatments have posited biological invasions (Invasion of the Body Snatchers), or cultural invasion (The Uplift Wars by David Brin).

The 1988 cult film They Live uses its own alien infiltration backstory as a satire on what some perceived as Ronald Reagan's America and the 1980s as an era of conspicuous consumption, in which the hidden aliens and human members of the elite oppress poverty-stricken humans and a shrinking middle class.

John Kessel makes use of the metaphor of alien invasion in his short story Invaders, by contrasting "the Krel's" (a fictional alien race) invasion of Earth with Francisco Pizarro's conquest of Peru, as if to illustrate the horror of the real event.

Alien invasion - Doctor Who