History Main / WarFromAnotherWorld

* ''ComicBook/BlackestNight'': The main plot is about the war between the [[OurZombiesAreDifferent Black Lantern Corps]] and all the rest of the Lantern Corps of the universe, who [[HeroRivalBaddieTeamUp have to team-up against their will to stop a bigger evil]] and not [[PlagueZombie become the next Black Lantern]]. In the last issues, the intergalactic war goes to Earth since [[spoiler:[[BigBad Nekron]] found the Entity of Life hidden on Earth, guiding all his Corps to Earth so he can eliminate it and all forms of life on the universe.]]

* ''Franchise/{{Transformers}}'' is often about the Autobots and Decepticons fighting on Earth, with humans being caught in the middle. The Michael Bay-directed ''Film/{{Transformers}}'' series has humans repeatedly change sides during the war. The first couple movies have them work alongside the Autobots after constant attacks by the Decepticons, even forming the N.E.S.T. government organization. The next couple movies show some humans turning on the Autobots, from those wanting them to leave and take the fighting someplace else to outright helping the Decepticons. The last few movies feature them hunting down both groups with only a few remaining loyal to the real heroes of the story. However, the humans never truly sided with Decepticons, except for Dylan Gould. In the first three movies they stand with Autobots. But after an Autobot betrays his fellow Cybertonians and Earth as whole, leading to millions dead, the humanity could no longer trust Autobots. In Age of Extinction humanity fights for itself, having Lockdown as a temporary ally. In Last Knight, humans once again stand for themselves, allying with Megatron only because he could deliver the weapon they were searching. However, then Cybertron arrives near Earth and Quintessa plans to destroy it, humans ally with Autobots once again to save their world. The first movie's tagline is even "'''Their''' war. '''Our''' world."

* ''WesternAnimation/TeenageMutantNinjaTurtles2003'': The Season 3 premiere, which consists of two back-to-back [[MultiPartEpisode Multi-Part Episodes]], is all about this trope as Earth finds itself caught in the crossfire of an EvilVersusEvil conflict between the Triceraton Empire and the [[HumanAliens Federation]]. Initially, the Triceratons [[AlienInvasion invade Earth]] as part of their hunt for the Fugitoid, a LivingMacGuffin who possesses the blueprints for a teleportation device that both sides seek to weaponize. Later, the Federation also gets involved and secretly make a deal with the US government to capture the Fugitoid. The three-part episodes where the two rival empires finally duke it out is appropriately titled "Worlds Collide".

* In ''LightNovel/TheRisingOfTheShieldHero'', the Four Heroes are all summoned via a magical ritual to the realm that the Kingdom of Melromarc is located, each of the heroes summoned from our world (or perhaps multiple, alternate versions of our world) with the goal of helping fend off the various monsters and magical threats that plague the land via the Waves of Calamity. The ritual equips them with their own magical, sacred weapons (a spear, a sword, a bow and a shield) that imbues them with uniques stats and abilities. [[spoiler:The Waves of Calamity are the result of two or more parallel worlds fusing together. Some of the worlds already have their own wars going on, which have now poured into the kingdom, resulting in even more chaos.]]

* ''Fanfic/AngelicResonance'': Although not a war, the story starts with the [[Franchise/LyricalNanoha Time-Space Administration Bureau's]] pursuit of the [[Manga/MagicalRecordLyricalNanohaForce Huckebein]] going horribly wrong and throws them in the [[Anime/CrossAnge Empire of Misurugi]]. The Bureau quickly pick up the First Princess and her maid abroad while the Eclipse-infected killers go on a rampage. [[spoiler:Then [[LightNovel/FullMetalPanic Leonard's Amalgam faction]] gets involved]].

* ''WesternAnimation/TeenageMutantNinjaTurtles2003'': The Season 3 premiere, which consists of two back-to-back [[MultiPartEpisode Multi-Part Episodes]], is all about this trope as Earth finds itself caught in the crossfire of an EvilVersusEvil conflict between the [[EverythingsBetterWithDinosaurs Triceraton Empire]] and the [[HumanAliens Federation]]. Initially, the Triceratons [[AlienInvasion invade Earth]] as part of their hunt for the Fugitoid, a LivingMacGuffin who possesses the blueprints for a teleportation device that both sides seek to weaponize. Later, the Federation also gets involved and secretly make a deal with the US government to capture the Fugitoid. The three-part episodes where the two rival empires finally duke it out is appropriately titled "Worlds Collide".

* ''ComicBook/BlackestNight'': The main plot is about the war between the [[OurZombiesAreDifferent Black Lantern Corps]] and all the rest of the Lantern Corps of the universe, who [[HeroRivalBaddieTeamUp have to team-up against their will to stop a bigger evil]] and not [[PlagueZombie become the next Black Lantern]]. In the last issues, the intergalactic war goes to Earth since [[spoiler:[[BigBad Nekron]] found the Entity of Life hidden on Earth, guiding all his Corps to Earth so he can eliminate it and [[KillEmAll all forms of life on the universe]].]]

** The first time was the [[OurOrcsAreDifferent Orcish Horde]] on [[DeathWorld Draenor]] -- [[TheLegionsOfHell twisted by the Burning Legion]] -- which fought a [[KillEmAll war of annihilation]] against the [[SpaceElves Draenei]] (in an attempt by the leaders of the Burning Legion to wipe them out for their "[[MoralMyopia betrayal]]" 50,000 years ago, which translates as "[[OmnicidalManiac not joining them in their war to eradicate all life in the universe]]") and eventually expanded the war into an invasion of Azeroth.

** [[spoiler:What really separates this apart from other series is how Aura is at least ten times more potent in Upper Earth than in Byston Well. Shou witnesses first hand that small missiles only made for destroying Aura Battlers have the power of mini-nukes, killing over a million people in Tokyo, and Aura Barriers are able to [[NoSell shake off nuclear weapons like nothing]]]]. The whole final arc is about the rebels stopping Drake before the world turns into a desolated wasteland.

* The ''VideoGame/SidMeiersAlphaCentauri'' expansion "Alien Crossfire". Two ships from warring factions of an alien race, the Manifold Caretakers and Manifold Usurpers, crash land on the same planet being colonized by humanity's remnants.

* In ''Literature/InvasionEarth'' by Creator/HarryHarrison, a group of alien ships requests aid from Earth against an incoming group of invaders. There is a big twist at the end. [[spoiler:Specifically, the two warring groups are actually working together. They're survivors from an ancient war between their races with no home to go back to. So they seek out primitive races to scam for radioactive materials, with one of the races pretending to be the good guys, and the other pretending to be the villains.]]

* In ''Literature/InvasionEarth'' by Creator/HarryHarrison, a group of alien ships requests aid from Earth against an incoming group of invaders. There is a big twist at the end.

* ''ComicBook/WildCATS'': This was the series' original concept, with agents of the good-coded Kherubim and evil-coded Daemonites fighting a SecretWar on Earth. Subsequently things got more complicated.