The alien invasion is a common theme in science fiction stories and film, in which extraterrestrials invade Earth either to exterminate and supplant human life, enslave it under a colonial system, to harvest humans for food, steal the planet's resources, or destroy the planet altogether.
The invasion scenario has been used as an allegory for a protest against military hegemony and the societal ills of the time. H.G. Wells' novel The War of the Worlds extended the invasion literature that was already common when science fiction was first emerging as a genre.
Prospects of invasion tended to vary with the state of current affairs, and current perceptions of threat. Alien invasion was a common metaphor in United States science fiction during the Cold War, illustrating the fears of foreign (e.g. Soviet Union) occupation and nuclear devastation of the American people. Examples of these stories include the short story The Liberation of Earth (1950) by William Tenn and the film The Invasion of the Body Snatchers (1956).
In the invasion trope, fictional aliens contacting Earth tend to either observe (sometimes using experiments) or invade, 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 a 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.
Technically, a human invasion of an alien species is also an alien invasion, as from the viewpoint of the aliens, humans are the aliens. Such stories are much rarer than stories about aliens attacking humans. Examples include the 1989 video game Phantasy Star II, the 2007 film Battle for Terra, The Martian Chronicles by Ray Bradbury, the Imperium of Man in the Warhammer 40,000 universe, Invaders from Earth by Robert Silverberg, the 2009 movies Planet 51 and Avatar and the 2011 movie Mars Needs Moms.
As well as being a subgenre of science fiction, these kinds of books can be considered a subgenre 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).
In 1898, H.G. Wells published The War of the Worlds, depicting the invasion of Victorian England by Martians equipped with advanced weaponry. It is now seen as the seminal alien invasion story and Wells is credited with establishing several extraterrestrial themes which were later greatly expanded by science fiction writers in the 20th Century, including first contact and war between planets and their differing species. There were, however, stories of aliens and alien invasion prior to publication of The War of the Worlds.
In 1727, Jonathan Swift published Gulliver's Travels. The tale included a race of beings similar but superior to humanity, who are obsessed with mathematics. They live on a four-and-one-half-miles-in-diameter flying island fortress called Laputa, and use its shadow to prevent sun and rain from reaching earthly nations over which it travels, ensuring they will pay tribute to the Laputians.
Voltaire's Micromégas (1752) includes two aliens, from Saturn and Sirius, who are of immense size and visit the Earth out of curiosity. Initially, they believe the planet is uninhabited, due to the difference in scale between them and human beings. When they discover the haughty Earth-centric views of Earth philosophers, they are very much amused by how important Earth beings think they are compared to actual titans such as themselves.
In 1892, Robert Potter, an Australian clergyman, published The Germ Growers in London. It describes a covert invasion by aliens who take on the appearance of human beings and attempt to develop a virulent disease to assist in their plans for global conquest. It was not widely read, and consequently Wells' vastly more successful novel is generally credited as the seminal alien invasion story.
Wells had already proposed another outcome for the alien invasion story in The War of the Worlds. When the Narrator meets the artilleryman the second time, the artilleryman imagines a future where humanity, hiding underground in sewers and tunnels, conducts a guerrilla war, fighting against the Martians for generations to come, and eventually, after learning how to duplicate Martian weapon technology, destroys the invaders and takes back the Earth.
Six weeks after publication of the novel, the Boston Post newspaper published another alien invasion story, an unauthorized sequel to The War of the Worlds, which turned the tables on the invaders. Edison's Conquest of Mars was written by Garrett P. Serviss, a now little-remembered writer, who described the famous inventor Thomas Edison leading a counterattack against the invaders on their home soil. Though this is actually a sequel to Fighters from Mars, a revised and unauthorised reprint of War of the Worlds, they both were first printed in the Boston Post in 1898.
The War of the Worlds was reprinted in the United States in 1927, before the Golden Age of science fiction, by Hugo Gernsback in Amazing Stories. John W. Campbell, another key editor of the era, and periodic short story writer, published several alien invasion stories in the 1930s. Many well-known science fiction writers were to follow, including Isaac Asimov, Arthur C. Clarke, Clifford Simak, plus Robert A. Heinlein who wrote The Puppet Masters in 1953.
The most well-known alien invasion scenarios involve the aliens landing on Earth, destroying or abducting people, fighting and defeating Earth's military forces, and then destroying Earth's major cities. Usually, the bulk of the story follows the battles between the invaders and Earth's armies, as in The War of the Worlds. However, not all alien invasion stories follow this plot. In some accounts, the alien invaders will covertly subvert human society using disguises, shapechanging, creating conflict in humanity and let humans destroy themselves, or human allies. In other depictions, the aliens score an overwhelming victory over humanity and the bulk of the story occurs after the aliens have taken over. Sometimes, the aliens do not come from space, but from another dimension, as is shown in the 2013 film Pacific Rim. Also in some fiction, the invaders may not actually be aliens, but demonic creatures from hell, or beings from the center of the Earth or even from Earth's far future.
This is a familiar variation on the alien invasion theme. In the infiltration scenario, the invaders will typically take human form and can move freely throughout human society, even to the point of taking control of command positions. The purpose of this may either be to take over the entire world through infiltration (Invasion of the Body Snatchers), or as advanced scouts meant to "soften up" Earth in preparation for a full-scale invasion by the aliens' conventional military (First Wave). This type of invasion usually emphasizes common fears during the Cold War, with the Communist agents suspected everywhere, but has also become common during any time of social change and unrest. The classic examples of this would be Invasion of the Body Snatchers, The Arrival, the gradual evolution of humans to ‘hybrid’ aliens in TV's Invasion, Threshold, the Animorphs series, Invader Zim, Robert A. Heinlein's The Puppet Masters and the John W. Campbell, Jr. short story "Who Goes There?", which was made into 1951 Howard Hawks film The Thing from Another World, with a more faithful adaptation being made by John Carpenter in 1982 as The Thing. Another film by John Carpenter "Village of the Damned", based on John Wyndham's "The Midwich Cuckoos" shows aliens living on Earth whilst masquerading as human children. In Doctor Who the Zygons attempt an invasion using their shapeshifting abilities. Later in the show and a spin-off, the Sarah Jane Adventures, the Slitheen - a criminal family from the planet Raxicoricofallapatorius - disguise themselves in human skin suits to infiltrate human society. Aliens could also control people to do their will through electronic devices implanted in human bodies such as in 1953's Invaders from Mars. Another example of alien infiltration is in the 2005 video game Destroy All Humans! in which the player controls an alien scout in order to destroy and eventually become the President of the United States, as well as annihilate humans in their path. In some cases, the aliens already look much like Humans - in the Star Trek franchise, in the 133 years before their participation in first contact in 2063, no fewer than six Vulcans spent significant amounts of time on Earth (though none were "invaders" - three were shipwreck survivors, the other half time travelers, in the company of at least one Human, from a future where their respective worlds were political allies), and were able to pass themselves as Human simply by using hair or hats to conceal their pointed ears; likewise the Bajoran Kira Nerys needed only to put a Band-Aid on her ridged nose, while at the same time the Trill Jadzia Dax was able to pass off her natural spots as tattoos.
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This is a theme that can occur in many invasion stories. In short, the alien invaders win and occupy the Earth or human civilization or they simply try to terraform Earth to make it livable as in The War Against the Chtorr (a more accurate term for this would be "xenoform"), at least until a human resistance movement overthrows the aliens and/or their puppet governments. Many occupation stories are influenced by the real human invasions by totalitarian governments, in which the alien invaders support existing human government infrastructures that welcome their new alien overlords or purge opposition governments and rebuild them in their own image and the enforcement of their rule through the use of collaborators and secret police. Examples of life under alien occupation can be seen in the TV series V, Falling Skies, John Christopher's book series, The Tripods, the comic book miniseries Slash Maraud, the video games of Half-Life, Call of Duty: Ghosts (in Extinction mode), and the Resistance series. In the Game Boy series of the Nintendo Comic Systems, the alien responsible for the conquest of Sarasland from the Super Mario Land series, Tatanga, wishes to conquer Earth with an iron fist and was able to conquer places anytime when he is released from the Game Boy, with successful occupations on places such as the World Trade Center, the Wonder World Mall, and the Great Wall of China. In the fictional history of the BBC science fiction programme Doctor Who, the genocidal Dalek race is heavily involved in invasion stories in the show, starting with The Dalek Invasion of Earth (though this story is set years after the invasion has actually happened). Most recently this happened in the universal Armageddon story "Journey's End". That story especially includes Daleks conquering the earth after moving it through space and then occupying it along with other stolen worlds to initiate their stratagem for universal destruction. L. Ron Hubbard's 1982 novel Battlefield Earth depicts a merciless alien race - the Psychlos - conquering and controlling Earth for 1,000 years to strip the planet of its minerals, mainly gold. The 2011 science fiction film, Battle: Los Angeles, depicts aliens invading Earth supposedly for water. In an episode of the action cartoon, Ben 10: Alien Force, one of the main villains, Vulcanus, buys a form allowing him to terraform Earth so he can drop a bomb into the center of the planet and have "all the comforts of home". Kevin, one of Ben Tennyson's friends, then says that Vulcanus' home planet is 850 degrees on a cool day.
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These are short-term alien invasions by creatures incapable of supporting a large-scale invasion due to small numbers who instead use the shock of their arrival to inspire terror. Other stories following this line of reasoning would have the alien invaders conducting reconnaissance and probing raids on the Earth's population and especially their military forces. Also, the invaders will try to choose isolated spots, such as the desert or farmlands of rural zones in the United States, as a staging area or landing zone. This type of plot line provides a better possibility of small groups, like local police and military, or even ordinary civilians, having the ability to repulse the invaders and return to normal life after the event. The 2002 film Signs is probably the most famous example of an alien raid movie. Because of budget constraints, this variation was fairly common in the 1950s science fiction B-movies, such as It Came from Outer Space, Teenagers from Outer Space, The Blob, and Plan 9 from Outer Space.
Beneficial alien invasion
This theme has also been explored in fiction on the rare occasion. With this type of story, the invaders, in a kind of little grey/green man's burden, colonize the planet in an effort to spread their culture and "civilize" the indigenous "barbaric" inhabitants or secretly watch and aid earthlings saving them from themselves. The former theme shares many traits with hostile occupation fiction, but the invaders tend to view the occupied peoples as students or equals rather than subjects and slaves. The latter theme of secret watcher is a paternalistic/maternalistic theme. In this fiction, the aliens intervene in human affairs to prevent them from destroying themselves, such as Klaatu and Gort in The Day the Earth Stood Still warning the leaders of Earth to abandon their warlike ways and join other space-faring civilizations else that they will destroy themselves or be destroyed by their interstellar union. Other examples of a beneficial alien invasion are Gene Roddenberry's The Questor Tapes movie and his 1968 Star Trek episode Assignment: Earth, Arthur C. Clarke's Childhood's End, the anime and novel series Crest of the Stars and David Brin's Uplift series of books.
The little grey/green man's burden idea was commonly explored by Harry Turtledove's Worldwar and Colonization series. The reptilian Lizard-men that invade Earth have an imperialist mindset comparable in the narrative to 19th century models of cultural imperialism. One of the moral dilemmas of the series, however, is that the Lizards are consistently portrayed as morally superior to Nazi Germany of the 1940s, which they are trying to invade along with the other Axis and Allied powers. The Lizards actually liberate Treblinka, and ethnic groups in Eastern Europe being oppressed by the Nazis hail them as liberators. They have difficulty conceptually understanding why the Nazis are committing ethnic genocide, and on the whole, consider humanity to be so barbaric and warlike that they would benefit from being united under their culture.
Demonic alien invasion
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In which the alien invaders are supernatural or otherwise religious-inspired demonic beings, who infiltrate the Earth, attack mankind, take over human society (disguised as humans themselves) and declare war upon the saints, fulfilling the events described in the Book of Revelation or another religious prophecy, occasionally invented for the story itself. Warhammer 40,000 and The Doom computer game series follows this concept. The novel Childhood's End may be viewed as a form of demonic alien invasion, because of the Overlords' devilish appearances.
Historical alien invasion
A period of the recent or distant past may serve as the scene of an alien invasion of one of the aforementioned types. One project of this kind is Harry Turtledove's alternative history Worldwar & Colonization series, where lizard-like aliens land on Earth in 1942, bent on conquest, forcing the opposing sides of the Second World War to sign hasty cease-fires and fight their own (largely) separate wars against the invaders.
In Sideslip by Ted White and Dave van Arnam, a private detective from our New York finds himself in an alternate reality where Earth is under occupation by interstellar humanoids nicknamed "Angels", who had landed in 1938, taking advantage of the confusion following Orson Welles' War of the Worlds radio program, and had ruled Earth as a colony ever since. In Starspawn by Kenneth Von Gunden, Earth is infiltrated by small parasitic aliens capable of attaching themselves to a human and controlling him or her - similar to the scenario of Heinlein's aforementioned The Puppet Masters - except that the invasion takes place in Medieval England, against the background of knights besieging a castle. In similar settings at Poul Anderson's The High Crusade, an alien ship lands at a Medieval English village, but the overconfident would-be conquerors find out the hard way that they are not immune to swords and arrows; the humans take over the ship and proceed to carve out an empire among the stars, but lose contact with Earth which goes on with its familiar history. In Eifelheim by Michael Flynn, an alien spaceship lands in central Europe in the middle of the Black Death.
In Doctor Who, because of the time travel element, historical invasions happen a lot, notably the Cyberman invasion of Victorian London, using a 60m tall cyber-king walker, in the episode The Next Doctor. Historical raids and alien contacts also feature in several stories, such as the Jon Pertwee episode The Time Warrior, in which a lone Sontaran makes a forced landing in mediaeval England, the Tom Baker episode Pyramids of Mars (in which the culture of ancient Egypt is shown to have been the result of the influence of visiting aliens, the Osirians, though this species did not invade Earth and imprisoned a criminal of their race Sutekh on Earth), the Peter Davison episode The Visitation in which crashed alien criminals are revealed to be indirectly responsible for the Great Fire of London, as well as the Matt Smith episodes where they determine "The Silence" had been controlling human civilization and progress since the beginning.
The Stargate franchise is based on this concept, where an alien race visited Earth and took on the mantle of ancient gods with the intent of capturing different groups of humans and sending them elsewhere to use as slave labor or corporal hosts. Much of the television program Stargate: SG-1 dealt with meeting descendants of such humans who had been transported across the galaxy and whose technological development evolved along different paths, as well as preventing the malicious aliens from attacking Earth.
The 1996 movie Star Trek: First Contact deals extensively with this theme, although the frame of reference is in the future; the Borg come to Earth in 2063, approximately two to three hundred years prior to the relevant events in the Star Trek universe.
This concept has also been explored outside of the film and novel forms of entertainment. The storyline of the video game series Resistance, where Earth had been invaded by an alien race that uses microbes to change the DNA of earth's inhabitants and biologically assimilates them into their hive-like society. From the point of invasion in the 1950s, Earth is spun into an alternate history setting that has yet to reach the date of 1960.
The Crysis series of games involves an alien race that has survived (possibly in suspended animation) underground for a very long time, and has only recently emerged to take over Earth in the context of the story. This is also a theme in the Transformers film franchise, though the motivations of the Cybertronian robots do not necessarily involve conquest.
Occasionally, two or more themes can be used as a combination. For example, the aliens may first infiltrate society secretly, then, after gaining human trust, they will suddenly begin destroying Earth's cities, with the humans taken by complete surprise. Another example of this is in two episodes of the popular sci-fi show Stargate SG-1 an alien race known as the Aschen befriend humans and share their advanced technology and medicine freely in exchange for stargate addresses. But it soon becomes clear that the Aschen plan to eradicate the human race slowly by making both women and men infertile so the human race dies out over generations. Another type of invasion is seen in various Godzilla films, most notably Destroy All Monsters, and also in the Monster Wars saga of Godzilla: The Series and the 2004 film, Godzilla: Final Wars. In these films, alien races take control of earth's monsters and use them to attack and destroy Earth's major cities, but are usually ironically defeated by the monsters themselves.
The online game, Cartoon Network Universe: FusionFall, uses the 'Alien Occupation' and a slightly different example of the 'Alien Infiltration' examples. In the game, Planet Fusion, ruled by the main villain Lord Fuse, has been travelling through space for 1000 years, consuming every inhabitable planet it encounters and finally reached its next target, Earth. Fuse then orders his Fusion Spawns to steal the most precious items of the Cartoon Network characters in order for Fuse to make Fusions (Evil versions of the main characters). The Fusions look almost exactly like their Earth counterparts, thus having the ability to trick the main characters into thinking they're human, not Fusion. (An example is when Fusion Bubbles tricked Professor Utonium into thinking she was the real Bubbles). Once Earth has been infected with the poisonous Fusion Matter enough, it will be ready to be consumed by Planet Fusion.
The classic treatment was The War of the Worlds by H. G. Wells, which was made into movies in 1953 and 2005, as well as 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 back story as a satire on 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.
In Doctor Who, alien invasions are sometimes the centerpiece of Earth-set episodes.
The beginning half of the popular video games Halo 2 and Halo 3 deals with the defense of Earth against a genocidal alien empire, the Covenant. The protagonist of the game along with Earth's military force, the UNSC, and a group of former Covenant who rebelled, the Covenant Separatists, eventually repel the invasion and topple the Covenant.
In the A.R. Curtis short story Best an invasion is portrayed more as a refuge accident, where aggressive cast-offs fight for supremacy against local police and civilians.
The Mass Effect franchise features a race of massive semi-organic sentient starships called Reapers who destroy any organic civilization advanced enough to devise artificial intelligence, based on the perceived inevitability of it rebelling. While the organic races featured in the series (e.g. humanity) are well in the space-faring stage of their development, the technological advantage of the Reapers is still overwhelming.
Alien invasions are a common element of the Godzilla movies, usually with a giant monster (such as King Ghidorah, Gigan, and Mechagodzilla) being used to attack major cities (usually Tokyo). Some movies have the aliens mind-controlling Earth's monsters and deploying them en masse to intimidate humanity. In all cases, though, the aliens are defeated by Godzilla and an ally.
In Orson Scott Card's series "Ender's Game", an insectoid race of hiveminded aliens known as the Formics invade Earth on two different occasions, known as the First and Second Formic Wars. The first invasion resulted in very few casualties, but the second resulted in tens of millions of deaths. After this second invasion, the conglomerate of nations known as the International Fleet decided to launch their own invasion that would completely devastate the Formic home planet.
Planetary defense in science fiction
Planetary defense against invasion is a recurring theme in science fiction, usually designed to repel an invasion of a planet by an external force; human or otherwise. An example would be during the Earth Alliance Civil War on the television series Babylon 5, whereby the loyalist forces used orbital planetary defense platforms to defend Earth from the separatist forces. Another good example is Independence Day which was a 1996 military science-fiction film, which had a central plot of a huge alien invasion to Earth´s major cities.
Planetary defenses are not limited to one pre-defined type, some are space or orbital based platforms or ships as in the previously stated example. Another example of planetary defense platforms is Cairo station, which is from the Halo 2 game and the Halo novels. As well as serving as docking stations for UNSC ships, MAC stations such as Cairo Station also possess a massive coilgun, which serve to ward off assaulting enemy fleets via long-range bombardments. UNSC worlds often possess multiple MAC stations in orbit, to provide overlapping fields of fire against either human or alien invaders.
There are also weapon systems based on the surface of planets occasionally, as in Stargate SG-1 where the hero uses an Ancient weapon in Antarctica to destroy the villain's invading fleet from the ground; others are simpler, including ground based fighters, as in the case in Star Wars Episode IV: A New Hope where single-manned fighters defended a rebel base against a moon-sized Death Star.
In addition, in the novel The Armageddon Inheritance from the author David Weber's Empire from the Ashes trilogy, Antarctica possesses a core-tap generator, which yanks large energy reserves from hyperspace and projects it around Earth as a planetary shield. While serving to ward off enemy fleets and bolster Earth's defenses against most conventional assaults, it proved insufficiently powerful against large asteroids and small moons, as when in the book the moon Iapetus was hurled at Earth to "crack it open like a bullet through butter." A similar shield is used to defend a rebel base in The Empire Strikes Back, but it was too small to cover the entire planet. As a result, while it was powerful enough to withstand the Imperial fleet's orbital bombardment, it was overcome by landing ground troops who destroyed the shield generator. However, when combined with the planetary defense platforms in place, planetary shields can be very necessary to planet-wide protection.
Some planetary defenses in science fiction are less fantastical than often proposed. For instance, the BBC television series Doctor Who has spawned two such examples, the fictional military organization UNIT stationed terrestrially to defend modern earth against invasion after the Great Intelligence attacked London in The Web of Fear, and a more secretive group Torchwood, who defend the United Kingdom against alien incursions. UNIT has appeared multiple times in Doctor Who when drastic events are involved, whilst Torchwood is the focus of a successful spin-off series.
The Legacy of the Aldenata series by John Ringo describe in detail a planetary defense scenario using alien technology to construct a fleet of starships. Similar themes can be seen in the Japanese anime series The Super Dimension Fortress Macross and its Robotech American adaptation. Both Macross and Robotech also include a "Grand Cannon" massive energy weapon based in the northern hemisphere that is used for planetary defense. Doc Travis S. Taylor's Warp Speed and The Quantum Connection books (known as The Warp War Series) gives examples of developing planetary defense systems based on warp technologies. The Von Neumann's War series by John Ringo and Travis S. Taylor also develops an organization designed to develop planetary defense strategies from present day technologies.
In Orson Scott Card's "Ender's Game" series, the "International Fleet" is formed by a conglomerate of nations in order to repel the Formic aliens who had invaded twice before. This organization chooses that, rather than defend the planet through the use of orbiting ships, they must execute a preemptive attack in order to defend their species effectively.
Another means of planetary self-defense in the face of an alien invasion is the use of a team of individuals assigned the duty of repelling or destroying the invasion force. Often this team is composed of a mixture of superheroes, superhumans, benevolent other worldly beings, or individuals with profound abilities in areas that may be applicable to fighting an alien army, such as marksmanship or hand-to-hand combat. An example of such a team combating an alien invasion fleet is in the film The Avengers (as well as in the same-titled comic books from which the film is based upon). In the film, the Avengers, a team of superheroes composed of Iron Man, Captain America, Thor, The Hulk, Black Widow and Hawkeye assemble together to defeat an alien army bent on subjugating Earth. Ultimately, the Avengers are successful in repelling and halting the invasion, and the Earth is saved from alien dominance.
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Invasion films were common in the 1950s featuring a variety of aliens portrayed as superior to earthlings both in intelligence and technology . In these films, aliens represent what some Americans feared about the Soviets. Invaders, friends or enemies, and often with the help of robots, either come to warn earthlings or destroy them with superior technology. Sometimes the invaders use the strategy of infiltration, taking over the minds of the people, making slaves of them or appropriating their bodies, thus making war unnecessary. In some instances the aliens already had a similar appearance - in Star Trek, while officially made contact with Humanity in 2063, (and were not "invaders" - some were shipwreck survivors, others time-travelers, accompanied by at least one Human, from a future where their respective worlds were allies) no fewer than six Vulcans had spent some time on Earth, passing as Human simply by using hair or skullcaps to conceal their pointed ears.
- Parrinder, Patrick (2001). "Estranged Invaders: The War of the Worlds". Learning from Other Worlds: Estrangement, Cognition, and the Politics of Science Fiction. Duke University Press. p. 143. ISBN 0-8223-2773-2.
- "Ender's Game". Publishers Weekly. Retrieved 2013-11-03.