Invasion

This Tag seeks to assemble a disparate collection of films in which the concept of invasion takes center stage. In this context, invasion refers to an incursion of unwelcome subjects - generally in large numbers - into an already occupied territory, and the resulting spread of invaders throughout that territory. For purposes of this Tag, these films mainly fall into the sci-fi/horror camp and feature protagonists forced to engage in a life-or-death struggle against an extremely dangerous enemy.

Although the list of potential invaders is practically endless, here are some frequently recurring general categories:

1. Extraterrestrial lifeforms: when sentient, technologically advanced aliens come to Earth, it's generally with a specific goal in mind (i.e., to conquer, subjugate, destroy, remove, or replace us). In the event that less sophisticated creatures happen to arrive, we'll instead see a disorderly series of attacks on unfortunate victims who find themselves in the wrong place at the wrong time.
2. Earthly plants or animals: invasive species or species with an accelerated reproductive cycle, mutants creatures arising from an eco-vengeance context.
3. Miscellaneous hard-to-classify beings, possibly but not necessarily extraterrestrial: synthetic beings/cyborgs, amorphous menaces (e.g., the inexorable gelatinous blob from 1958's "The Blob" or the deadly cream-like substance from 1985's "The Stuff"), or even inorganic invaders (e.g., the rocks from 1957's "The Monolith Monsters" or the silicates from 1966's "Island of Terror").
4. Supernatural horrors: demons, spirits, evil imps and similar supernatural beings.

 
Invasions themselves can boldly occur in broad daylight or be carried out surruptitiously, such as the case in the classic "Invasion of the Body Snatchers" (1956, Don Siegel). Some invasions can also take an even more disturbing turn, such as when a corrupt contingent of humanity turns out to be in cahoots with the alien invaders, as in John Carpenter's "They Live" (1988).