Great Offscreen War

There was a war. It happened years ago, maybe even thousands of years. Characters reference it, especially if they took a part in it: the Shell-Shocked Veteran never managed to get over what he experienced back then, while the Phony Veteran, on the other hand, will never shut up about how many brave things he did in it.

Sometimes people will use the war as a reference point for placing events on a timeline - something happened a few years before the war, or somebody did something after the war.

Maybe people still have to deal with its consequences. The war happened, and it left its ugly mark on the world. But it's never shown to the audience - we never see a single Flash Back from the war, are never shown more than just a glimpse of what happened. The war will be referenced, but otherwise left mysterious, unexplained. Why it happened, how it ended, and what all the things that took place there (which people talk about like it should be obvious) actually were, are never explained. The war is only a mysterious event of the past, included mostly to add a bit of mystery and give people excuses for insane ideas. Needless to say, this trope can easily be processed into Fanfic Fuel

World War Three is often used as this, as are the Fourth, Fifth, Sixth and so on. For that matter, so are the First and Second. Stories set After the End have the tendency to do this with the war that caused the apocalypse. If the war never stopped, may be a Forever War.

If said war is going on presently but the characters themselves aren't involved, then it is Behind the Black.

Often used as a sub-trope of Cryptic Background Reference. Compare also Cataclysm Backstory.

Please, avoid shows referencing Real Life conflicts: we have much more information about them than will be ever provided in the typical case of the fictional conflicts mentioned here, so they don't count for the 'mysterious/unexplained' element of the Great Offscreen War.

Anime and Manga

 * The war with the Quincies in Bleach.
 * The Ghost in the Shell TV series is set sometime after both World War III and IV.
 * Code Geass has the Britannian invasion and conquest of Japan, which we see only in flashbacks concerning young Lelouch, Suzaku and Nunally and the one from first episode opening sequence. There also was an alternate version of the Napolean wars, where Napoleon conquered Great Britain, making all the British aristocracy run to America, creating the Britannia Empire.
 * The many wars of the Ancient Belka in Lyrical Nanoha. We have been told some general info about it, such as how it destroyed Old Belka and led to the current age where physical-based weapons were banned, but otherwise, it's a big question mark. As Nanoha Vivid revolves around the Reincarnation of two prominent figures from that war, many readers hope that it will eventually give more insight to that period.
 * Cowboy Bebop has the War on Titan, which shaped the lives of Spike, Vincent, and Grencia years before any action related to the main story took place. We get a few glimpses of it in flashbacks however.
 * Last Exile also has the war between its two major powers, which is mediated by The Guild. Much of the action of this war takes place BEFORE the actual story, as a few episodes in we discover that
 * In Blue Gender, we don't actually see humanity get overtaken by the Blues.
 * The War with "Them" in So Ra No Wo To is a complete mystery that has become filled with myths.
 * Mysterious conflict with Mazinkaiser SKL, whose conseqences are related to events of the series.
 * Naruto has the first three Great Shinobi Wars in backstory. All we know is Konoha won the 3rd one against Iwa, which Kakashi's team fought in, and many, many lives were lost during all three.
 * The war between Megalomesembria and Hellas Empire in Mahou Sensei Negima.
 * Pumpkin Scissors begins with the graduation ceremony of a class of army cadets being interrupted by an announcement that the war everyone thought they were going to be sent to fight in had just ended. The series itself is about a team working to help repair all the damage that was inflicted on their country during the war.
 * The war between the  in Tengen Toppa Gurren Lagann. Parallel Works #8 details this a little focusing on Lordgenome's involvement.
 * In Neon Genesis Evangelion several wars broke out a few days after the Second Impact, one of which resulted in the destruction of Tokyo. We know nothing about these wars other than what's mentioned in Shinji's history textbook.

Comic Books

 * Star Wars Legacy has the conflict between Galactic Republic and Empire, won by the latter, who then got into the war with the Sith.
 * Venado Bay in Legion of Super-Heroes V4.
 * In the second arc of The Authority, Jenny Sparks mentions how Earth cut down all connection with the alternate Universe, The Sliding Albion, after the First World War erupted there. Characters from Albion mention briefly that between that event and Albion's invasion on Earth, that world has seen eight other world wars.
 * Also, the fourth story arc (and first written by Mark Millar) showed us a glimpse of another alternate Earth, which had thirteen continents. A world war that erupted there ended with armies of Adolf X exterminating all non-black people on all of them. The Engineer finds the idea of sending a group of superpowered white supremacists there quite interesting.

Fan Works

 * The Private War in The Jackson Legacy takes place a decade before the story kicks off.
 * In With Strings Attached, Grunnel talks about how the Tayhil and their monsters conquered most of Baravada some 200 years ago, and how the skahs rose up to take back the place.
 * There are several references in Drunkard's Walk to the "Vampire War" which took place in main character Doug Sangnoir's home world some time before the start of the story.
 * Kimi no Na Iowa has not one but two of these. First and further back is some vaguely alluded-to mess with "Yamata" that is strongly implied to be but never outright confirmed as the events of Debt of Honor, given various Japanese characters' talking about the stains it left on Japan. Second is a "Terror" that Ended over a decade ago, but not before badly impacting the Middle East.

Film

 * The Clone Wars were this for the Star Wars trilogy until the prequels came, then two cartoons and a lot of other things that explored it, so it ultimately avoids this trope.
 * When watching Airplane!, they never make clear which war "The War" was for Ted Stryker, though judging by when the movie was made, one might assume Vietnam. As farcical as the entire movie is, it could very well have been some other war entirely though. Hell it could be a war they (or Ted) completely made up as well.
 * "The War" in Zero Hour!, the film on which Airplane! is based, and which came out a quarter of a century earlier, was obviously World War II. This timeframe informs a lot of the gags and references in the latter film.
 * The Lord of the Rings begins with Galadriel recounting the story of the last war with Sauron, several thousand years prior. We only see the end of the final battle.
 * The Time Machine (1960): In-Universe. The protagonist from 1899 traveled a couple of decades into the future. One of his friends' sons mention "the front" of "the war". It's obvious its the First World War, but being a time-traveler, he was unaware.

Literature

 * The Discworld series has two examples - the wizard wars which serve as an example of why wizards shouldn't actually cast spells, and the wars of the Evil Empire, which serve as the origin story of the Orcs.
 * The First Wizarding War against Voldemort in the Harry Potter books.
 * The war against Gellert Grindelwald is even more obscure. All we know for sure is that it apparently took place around the same time as World War II. Fanon consensus is that Grindelwald and Those Wacky Nazis had some sort of alliance.
 * Twice in The Hunger Games: the civilizational collapse that led to the founding of Panem, and the more recent "Dark Days" when Panem's provinces rose in an unsuccessful rebellion against the Capitol.
 * Shakespeare's As You Like It: Duke Senior was (somehow) deposed by his younger brother Fredrick and exiled to the Forest of Arden. A very blatant Deus Ex Machina at the end restores Senior to his rightful place.
 * Also Old Hamlet's war with Norway in Hamlet.
 * Othello's military record might also count: he boasts at length of his experience with 'pride, pomp and circumstance of glorious war', but we never see him fight.
 * Macbeth begins with a recounting of a war between Scotland and Norway.
 * The Butlerian Jihad is repeatedly mentioned in the original Dune series and had a profound effect upon the setting. After Frank Herbert's death, his son Brian and Kevin J. Anderson wrote a prequel trilogy to flesh out the details. But the fans try not to talk about those.
 * Besides the war, the trilogy also serves to conveniently set up most of the major players in the original Dune 'verse, such as the Corrino Imperium, the House of Atreides, the House of Harkonnen, the Spacing Guild, the Bene Gesserit, the Suk Inner School, and the mentats.
 * Bujold's Vorkosigan Saga is full of these. Mad Yuri's War, the Cetagandan Invasion, the Komarr Conquest and subsequent Revolt all have a direct impact on the storyline decades after they took place.
 * The Psychlo invasion in Battlefield Earth, which lasted about 9 minutes.
 * In Sergey Lukyanenko's Watches books, the Treaty is signed between the Light and the Dark Others after a magical war that nearly destroyed everything. Hardly any details are revealed about the war. The beginning of The Film of the Book Night Watch shows a battle between two groups of barbaric-looking people without using any magic (the director hates magic), with each group consisting of two dozen men at most. This is likely meant to be symbolic, though.
 * Larry Niven's Future History (leading to Known Space) series deals heavily with relations between humans and the Kzin, but the early Man-Kzin Wars never showed up in the books just because Niven didn't like writing war stories. He did let other writers go back and fill that in later, though.
 * The aptly-named Vague War in Sergey Lukyanenko's Line of Delirium, which takes place decades prior to the novel. Many references are made to the war, but few details are revealed. Apparently, it was a big free-for-all with all known races but no alliances. The war led to the formation of the Human Empire. The author even throws in a funny story about humans spreading misinformation about their dietary needs (i.e. that we need spinach to survive). The aliens spend resources developing a spinach-killing virus and lose countless ships spreading it throughout the human worlds. When humans don't die, they surrender out of shock. On a less funny note, good luck finding spinach after the war.
 * The Aiel War in The Wheel of Time is mentioned in passing by numerous veteran Warders, Tam al'Thor, and others. Many other wars - the Breaking of the World, the War of a Hundred Years, Artur Hawkwings war of consolidation, all serve to create rich background for the series.
 * A Song of Ice and Fire has many of these. The most important is Robert's Rebellion, which is really the cause for all of the events in the series - giving the effect that the reader has plunged into the middle of the story rather than the end. The Blackfyre Rebellion also, and the Doom of Valyria (which is seldom mentioned in more detail than its name) are further back in time.
 * Also, whatever it was that Tywin Lannister did the to inspire 'The Rains of Castamere'. "But there are no Reynes and Tarbecks"... "Exactly."
 * From Honor Harrington:
 * Admiral Theisman's purge of the State Sec forces which refused to fall in line with the new government after the overthrow of the Committee of Public Safety. The only part of it shown is from The Fanatic, which itself took place away from the meat of the action. Not a typical example, as that particular conflict took place between two of the later books of the series.
 * Earth's "Final War" many centuries before the current timeline, where the planet was nearly rendered completely uninhabitable until several colonies sent aid to repair the damage.
 * In Jo Walton's Alternate History Small Change trilogy, Germany continued fighting on the Eastern Front past 1949; Japan conquered most of China. The novels take place from the detached perspective of England, with word of the continuing war coming in newspaper headlines and occasional chatter.
 * Stephen King's Dark Tower books occasionally reference the last war of the Gunslingers against the Good Man, and it's the backdrop against which Wizard And Glass is set. There is also an even older event implied to be a nuclear war, which is why the series is After the End in the first place.
 * In the Star Trek: New Frontier series, Calhoun and Picard (and their crews) discover that a species that's apparently been friendly is actually capable of an insidious level of mind control which they've hid successfully until then. In the next book in the series, there's been a Time Skip of several years and said alien species has been defeated after a fairly vicious war.
 * Triplanetary mentions the first and fourth Jovian Wars, which resulted in the formation of the Triplanetary League from Venus, Tellus, and Mars.
 * The 'Holy War' against the Ghouls in E. R. Eddison's The Worm Ouroboros, in which all the civilized ("polite") nations of the world of Mercury fought alongside each other, and that ended just shortly before the book's storyline begins.

Live Action TV
"Doctor: You weren’t there in the final days of the war. You never saw what was born. But if the Time Lock’s broken then everything’s coming through, not just the Daleks, but the Skaro Degradations, the Horde of Travesties, the Nightmare child, the Could-Have-Been-King with his Army of Meanwhiles and Never Weres – the war turning to Hell!"
 * The Last Great Time War from Doctor Who. It was never shown, we know only that it caused a lot of destruction and wiped out entire races, including the Time Lords, whose last survivor was the Doctor. We find out that the Doctor was the one who ended the war, killing every Dalek (apart from a few who got away, of course) at the cost of also killing every Time Lord, including his own children and grandchildren. The Doctor has to deal with the consequences of the Time War from time to time and sometimes he or somebody else makes a reference to some events of it, but it's still mostly a mystery.
 * Current showrunner Steven Moffat has gone on record saying that he will never show the Time War since there isn't enough money in the world to do it justice.


 * Older episodes referred to similar such events, including the survivors of the destruction of Phaester Osiris defeating Sutekh and sealing him in a pyramid on Mars, or the ancient war between the Time Lords and the vampires shortly after the beginning of time.
 * Ancient battles between the Fledgling Empires (including Gallifrey) and the Racnoss were mentioned in "The Runaway Bride".
 * The Sontarans have been at war with the Rutan host for at least 60,000 years of the Whoniverse's timeline (mentioned in both Doctor Who and The Sarah Jane Adventures), and yet we've never encountered a Rutan or Sontaran together on TV once.
 * Played With in "The Doctor's Daughter". A war, fuelled by cloning machines, has gone on for 700 generations. It turns out that those 700 generations were cloned, shoved into battle and killed in the space of.
 * Star Trek has a lot of those.
 * The Third World War and Eugenic Wars, all taking place on Earth and concerning only humanity. It was actually one war in the Original Series, but was later divided.
 * There are EU novels dealing with both, with The Rise and Fall of Khan Noonien Singh being the most prominent. Also, in the interest of reconciling the Eugenics Wars with the real life passage of the era in which they are said to have taken place (1990s), the Eugenics Wars were retconned into a far less grand scale war that happened mostly in the shadows of real life events.
 * The war between the Federation and Romulan Empire, which forms the backstory for the episode "Balance of Terror".
 * The ongoing war between the Federation and the Klingons at the time of the Original Series is mostly not shown.
 * Note that the Federation and the Klingons have gone to war many, many times: A few of these conflicts have been depicted on-screen, including in the Original Series: The brief Federation-Klingon War of 2267 (which was ended by the Organian Peace Treaty, imposed upon the belligerents against their will) took place entirely within the episode "Errand of Mercy". Another Federation-Klingon War took place during the first half of the fifth season of Deep Space Nine, which was effectively ended (and the terminated alliance suddenly restored) when the Cardassians joined the Dominion.
 * The Next Generation has the war between the Federation and the Cardassians, which was responsible for creating the Anti-Cardassian Maquis. Strangely, it wasn't mentioned in the first seasons, only later.
 * In Star Trek: Insurrection, the Dominion War is treated like this.
 * As well as "brutal border wars" against the Talarians and the Tzenkethi, which happened at some point between the Original Series and the next Generation.
 * The Earth-Romulan war ended as this, because Enterprise was cancelled before it could cover it. The continuation novels have since stepped in to flesh it out.
 * When first mentioned in the original series, this war was fought entirely at extreme ranges with nuclear weapons (and with neither race ever actually seeing a member of the other).
 * Both series of Battlestar Galactica have mentioned previous wars with Cylons.
 * However, the new BSG's First Cylon War will be getting screentime in the upcoming Blood and Chrome series. A licensed video game also purports to cover that period, even being played from the perspective of Commander Adama as a rookie pilot, but it mixes and matches so many elements of the original series and remake that it probably belongs in its own separate continuity.
 * Silicate War, the war with the android revolution, taking place years before events of Space: Above and Beyond.
 * The conflict between Dharma Initiative and the Others was only hinted at in the first four seasons of Lost, though the Season 5 gives us a pretty clear picture of it. The conflict between the Others and the US Army is even more obscure.
 * The war with the Magogs from Andromeda, the end of which caused the Nietzschean revolution, may count too, as it started at the beginning of the first episode. The episode then jumps 300 years in the future, to the main plot, not only skipping the downfall of the revolution, but also the civil war among the ones who caused it, the High Guard.
 * Played with in That Mitchell and Webb Look where a group of people are holed up in a nuclear bunker playing a game show and broadcasting in the vain hope somebody is actually watching. It all focuses around "The Event"; the only interesting thing any of the characters can think about but are sworn not to talk about for various reasons. The most probable event would be a nuclear war.
 * Or alternatively whatever caused the majority of the human population to become zombies ('Them').
 * Babylon 5 has the Dilgar War, the first major interstellar war that the humans got involved in, as well as the previous Shadow War, which took place around a thousand years previously. We do see a glimpse of that era, mostly just some less advanced looking Minbari ships, but nothing of the war itself.
 * Also the Telepath War. We are shown only before and after.
 * And the first Narn war for independence from the Centauri, about 100 years prior to the beginning of the series.
 * Along with the numerous wars the Centauri Republic was waging with its neighbors in the third season, none of which are seen, or indeed the numerous smaller wars between the members of the League of Nonaligned Worlds in the same season.
 * There are also allusions to various minor conflicts that the Earth Alliance took part in. Not to mention the Earth Minbari War, which we heard much about, but saw little of, until the prequel movie In The Beginning.
 * Power Rangers falls back on this one a lot, to the point where Epileptic Trees have grown due to some wars sharing the same rough dates:
 * Mighty Morphin Power Rangers had a great battle between Good and Evil 10,000 years ago. Zordon was with the good guys, Rita with the bad guys under the command of Zedd. We have no other clues about it beyond that, despite the many ancient magical characters who were there and make none-too-informative references to it.
 * Power Rangers Lost Galaxy is so vague that we don't even know if there was one big event or just a bunch of isolated incidents. Either way, a lot of backstory happened 3,000 years ago.
 * Power Rangers Lightspeed Rescue had Bansheera and company put in the can 5,000 years ago. Her entire motivation for attacking in the present is to destroy the city and reestablish her palace upon the demons' sacred ground, granting 'ultimate power.' The fact that she had it then meant she had to have been a lot worse than anything witnessed during the Lightspeed series.
 * Power Rangers Wild Force had the war between the Animarian civilization and the Orgs 3,000 years ago.
 * Power Rangers Ninja Storm introduced one of the generals this way; the warlord Shimazu terrorized the populace with his Wolfblades 2,000 years ago until he is sealed in a mask.
 * Power Rangers Mystic Force saw a group of wizards seal away the forces of the underworld only twenty or so years prior.
 * Power Rangers Jungle Fury had a war between man and beast 10,000 years ago. Surprisingly, the four of the seven Old Masters that survived the war also survived to the present day.
 * Averted in Power Rangers RPM, where we get a number of flashbacks to Venjix's conquest of Earth the year prior.
 * Power Rangers Samurai had the Nighlocks sealed away by samurai in feudal Japan, and apparently a number of skirmishes between them and the samurai's descendants in the intervening years.
 * In The Walking Dead, the military is mentioned to have been overtaken by the Walkers and their abandoned equipment and corpses are seen lying about in the streets of Atlanta and outside of CDC, but it's never shown how the military were defeated.
 * The Firefly pilot (and one other episode) contain a flashback to the "Independence War", but other than that it's just talked about, although its aftermath is the prime motivation for many of the characters.
 * Kamen Rider has an unusual example: Kamen Rider Agito is a non-direct sequel to Kamen Rider Kuuga, most explicitly referenced by the police-made G3 Powered Armor being based on data from Kuuga himself. According to the backstory, Kuuga's old enemies the Grongi fought a war against another monster group, the Lords, who eventually won and became the villains of Agito. Kamen Rider Decade directly references this when the heroes go to an Alternate Universe version of Agito and land right near the end of the Grongi-Lord War.
 * And of course then there are things like the Rinto Kuuga's battle with the Grongi, the Battle Royale, and the original OOO's battle with the Greed, though that one is not what it seems.
 * In Merlin there are increasingly frequent mentions of a war waged some time before/around King Uther's time in which Ancient Kings were pitted against the High Priestesses.

Tabletop RPG

 * Dungeons & Dragons adventure I12 Egg of the Phoenix. The War of Ending between the forces of Evil and Old Empyrea. Doc and the silver dragon Falx fought in the war, during the adventure the PCs find a message that dates back to it, and one mission involves scouting one of the Castles of Ruling that played a major part in the war.
 * The Points of Light settings in 4th Edition has the war between the civilization of Nerath led by King Elidyr and the gnoll demon horde headed by Yeenoghu. There was also the war between the tiefling (half-devil) empire of Bael Turath versus the dragonborn empire of Archosia. Your characters most likely will start their career scrounging leftover supplies from said wars.
 * Warhammer 40,000 includes a lot of this in the Backstory, such as a Robot War that explains the Imperium's distrust of Artificial Intelligence.
 * Exalted has a few examples: the Primordial War, the Aftershock War, the Usurpation and the Balorian Crusade. All of these are provided some level of detail (specifically who was fighting and why), but the exact events of the wars are generally shrouded in mystery (typically because they all involved reality being damaged to some degree).
 * And those are just wars involving the Exalted. The occasional hint is dropped regarding wars waged by gods in the era before humanity, and even occasionally to conflicts involving the Primordials prior to the existence of Creation.

Video Games

 * Castlevania has "The Demon Castle War" in 1999 where modern-day soldiers attacked (and died; given the zombies) Dracula's Castle. This war also heralded Dracula's true and final death. There is no game that covers this.
 * Freelancer has the Coalition/Alliance war, the beginning of which was shown in Starlancer but which lasted for another century afterward and the winner is not the one the first game would indicate, as well as the 80 Years War between Rheinland and the GMG.
 * Star Wars Knights of the Old Republic has the Mandalorian Wars. Much of the information about it is from allusions and As You Know statements in the games, and lots of characters you run into in both games are war heroes or veterans from one side or the other.
 * For the longest time, StarCraft had the Guild Wars, which were referenced only in vague snippets as a civil war whose consequences still loomed over the Terran worlds. Fast forward many years, it's been more-or-less explained away with tie-in literature. Still nothing in the games, though.
 * Cave Story: References are made several times to a war for control of the Demon Crown. It's implied that the protagonist and Curly Brace were combatants in this war, two of the few surviving soldiers from the army that massacred the Mimigas.
 * Guild Wars: Prophecies has the actual Guild Wars, Factions has the Tengu Wars, Nightfall has the war against Palawa Joko.
 * City of Heroes has the first Rikti War in Primal Earth, and the Hamidon Wars in Praetorian Earth.
 * Mass Effect has numerous wars in its long history: the Rachni War, the Krogan Rebellions, the Morning War, the First Contact War, the Skyllian Blitz and.
 * Metal Wolf Chaos: The Arizona Conflict
 * BlazBlue: The First War of Magic, in which humans (including Hakumen, Jubei, Valkenhayn, and Terumi) fought against The Black Beast. Later, the Ikaruga Civil War, in which Jin became "The Hero of Ikaruga" by murdering Bang's lord.
 * Guilty Gear has Gear War, apocalyptic conflict between humans and Gears, led by Justice. In some games you can play duels that happened back then.
 * The Seven Hour War from Half Life 2.
 * In the Ground Control games: World War 3, the Independence Wars, the First Stellar War, the Terran-Viron conflict, most of the Second Stellar War. There are mentioned in a few brief lines in the manual.
 * In the Earth series, we never get to see or read details about World War 3, only that it was a Nuclear War that destroyed all former nation-states. Only a few facts are known from before the war, mostly about the founding of the Lunar Corporation. The game history starts after the war, with the creations of the United Civilized States and the Eurasian Dynasty.
 * In Nexus: The Jupiter Incident, the AI Wars are mentioned, but no details are given. Other conflicts not mentioned or mentioned/shown only briefly are the war between IASA and the megacorporations, the Vardrag-Gorg War, and the Noah-Gorg War prior to the events of the game.
 * The Great Keyblade War in Kingdom Hearts, which took place some time before the prequel,Birth by Sleep, and reshaped the game's whole universe. All that remains is an absolutely massive Field of Keyblades on an otherwise abandoned world.
 * The Legend of Zelda Ocarina of Time has a vague recounting of a war which occurred before Link was born and led to the death of his mother, who left him in the care of the Great Deku Tree. It's implied that this was the war that led to the unification of Hyrule.
 * The Legend of Zelda a Link To T He Past talks about a war known as the Imprisoning War in which the Knights of Hyrule fought to give the Seven Sages the opportunity to seal Ganon in the Sacred Realm.
 * The Legend of Zelda Twilight Princess mentions a similar conflict, describing how an evil tribe of powerful sorcerers (known in Fanon as the Dark Interlopers) came so close to getting the Triforce that the Spirits of Light had to entrap them in the Twilight Realm, where they evolved into the Twili.
 * The Legend of Zelda Skyward Sword mentions an earlier conflict in which Hylia and her armies fought against armies of invading demons to keep the Triforce safe. In this case, the offscreen nature of the war is actually justified: in the early days of the war, the group from whose perspective we see were sent up into the sky on a Floating Continent with the Triforce to keep both safe and out of reach of the war.
 * At the start of Metroid Prime 3: Corruption, a Federation technician mentions that he hasn't seen "that many fighters scrambled since the Horus Heresy Rebellion.
 * Fallout has the Great War, a two-hour war during which every nuclear-capable country in the world launched. No one knows who launched first.
 * Two sources - the leader of the remnants of the US government and the log of a Chinese submarine commander during the Great War - point to the Chinese. Still, they might be mistaken, and part of the lead-up to the Great War is still undetailed - the war between China and the USA have been given a fair bit of attention, but the other Resource Wars - especially the one between Europe and the Middle East, and the ones that happened in Europe after that - are still mostly names, if even that.
 * Also the theory that a bored AI started it.
 * Loghain of Dragon Age Origins often mentions the Ferelden rebellion against Orlais. Vague references to the war between the Qunari and the Tevinter Imperium are also present.
 * The first blight lasted 192 years, the second lasted 90 years: the third and fourth blight were comparatively smaller and lasted only 15 and 12 years. At the beginning of origin, Duncan is desperatly trying to increase the ranks od the Fereldan Grey Wardens in order to avoid another blight lasting years or even generation.
 * The plot of Dragon Age II is about what started the Mage-Templar War that has engulfed all of Thedas by 9:40 Dragon. Vague hints are all we actually know about the present in which the framing-device is set in, whereas the game itself focuses on the life of Hawke from 9:30 - 9:37 Dragon and how they came to unintentionally participate in the opening shots of the conflict.
 * The First Eptinan Wars exist has only a blurb in the manual for Vanguard Bandits. The Second, also has this effect, having been going on since before the game starts, and despite still going on most of the backstory for it exists in a single flashback.
 * Square Enix seems to love this trope:
 * Final Fantasy VI: The War of The Magi that destroyed previous civilization(s) and petrified the Warring Triad, goddesses of magic.
 * Final Fantasy VII: The war in which Shinra conquered the world, especially Wutai. The very end of this war (the conquest of Wutai part) is the very first chapter of Crisis Core.
 * Final Fantasy VIII: The war between Galbadia and Esthar, roughly eighteen years before the game began, which was caused by Sorceress Adel, the ruler of Esthar, attempting to Take Over the World.
 * Final Fantasy X: The war that destroyed the world and drove Yu Yevon mad, turning him into a mindless summoner.
 * Final Fantasy XIII: The War of Transgression, which nearly destroyed Cocoon thirteen centuries ago.
 * Final Fantasy Tactics: The war fought between Murond and the Zodiac Braves. And recently, the 50 Year War in which many of the game's older famous generals made a name for themselves.
 * Dissidia Final Fantasy: The war between Lufenian and their neighbor, which facilitated the birth of Chaos to defeat Omega.
 * Touhou: The Great Suwa War, in which Kanako subjugated Suwako; and Yukari's (first) invasion of the Moon.
 * Your milage may vary on
 * The Belkan War was this in Ace Combat 5 The Unsung War: the only events mentioned in the game were that Bartlett and Pops were shot down together, and that it ended when Belka dropped seven nukes on its own soil. It was later expanded on in Ace Combat Zero.
 * Since Grand Theft Auto 3 radio conversations and ads have hinted at a war between America and Australia which happened sometime in the mid 1980s. It's played for laughs.
 * Septerra Core. The Resource Wars, the most recent of the wars between Ankara and Jinam. Also the war between Chosen factions that devastated Maya's hometown.
 * The Ura-Caelondia war in Bastion. It's been over for a while, but a lot of the Ura and the only living Caelondian old enough to remember it (Rucks) are still a bit sore over it.
 * Tales of Vesperia references The Great War between humans and Entelexeia. One of the party members is a veteran.
 * The Fire Emblem Elibe games (being the 6th and 7th titles) had a great war between humans and dragons, referred to as 'The Scouring' that occurred roughly 1000 years before the events of the games. It ended with the humans supposedly killing off the dragons, when, in actuality, the dragons, on the verge of defeat, exiled themselves to the land of Arcadia, closing the gate portal behind them.
 * In Ultima VI, there's supposedly a huge war with the gargoyles going on. The soldiers talk about it. You see the wounded being cared for in Cove... however due to the Wide Open Sandbox gameplay you travel all over the fairly pristine world and never find a single battleground.
 * Dungeons of Dredmor contains many references to a war between elves and dwarves that's taken place back on the surface; the dungeons are full of discarded weaponry and such.
 * In The Elder Scrolls series there have been many wars in its backstory, but only three act as direct backdrops for main quests. The first was the War of the First Council (culminating in the Battle of Red Mountain), taking place thousands of years ago, which saw the disappearance of the Dwarves and the Tribunal's (plus Dagoth Ur's) rise to divinity, setting the stage for Morrowind. The second was Tiber Septim's conquest of Tamriel, aided by Daggerfall's giant mecha MacGuffin, Numidium, and the third was the The Great War, which took place between Oblivion and Skyrim and set up the entire civil war plotline.
 * Ar tonelico series: the war between Sol Ciel and Sol Cluster that peaked with Grathnode Inferia. Much of the events of the war has passed into legends, chronicled in Ar=Ciel Ar=Dor.
 * Ar tonelico 1 has the war between Mir-led Reyvateil and humans, which ended with Mir sealed and the Reyvateil treated as second- or even third-class citizens.
 * Ar tonelico 2 has the previous period of conflict between the Grand Bell and the Sacred Army. The current period of conflict takes the majority of the gameplay, so it doesn't feel very offscreen-y.
 * The Assassin's Creed series makes reference to a war that occurred tens of thousands of years ago in the First Civilization, between Those Who Came Before and the humans they used as slaves. This war is never detailed, but is instead used as a context to explain how the Half Human Hybrids "Adam and Eve" became Phlebotinum Rebels and stole the secret of the Pieces of Eden. And then their civilization was wiped out by a solar flare, making the whole thing moot.
 * Hexx mentions the Chaos wars, which apparently involved one of the four deities in the setting.
 * The X Universe backstory includes the Terraformer War in the 2140s AD, during which insane terraforming robots wiped out all of Earth's extrasolar colonies and nearly destroyed Earth, too. A Terran warfleet managed to lure them through a jumpgate, which was then destroyed behind them; this fleet became the Argon race. About 200 years later, we had the First Xenon Conflict, where the terraformers reappeared, followed by the Boron Campaign, a more conventional interstellar war between the various superpowers.
 * Lt. Surge in Pokémon Red and Blue refers to a war in which his electric Pokémon "zapped [his] enemies into paralysis." None of the subsequent games (except the remakes, which repeated the line exactly) mentioned anything about this war.

Web Comics

 * Ronin Galaxy: Taylor speaks to cecil about the current war-like state of Earth and her difficulty getting to the Moon on this page. Cecil retorts that Earth is an "antique collecting space dust."
 * One (probably two) of the four "Breakings" from The Dragon Doctors.
 * The war with the Other in Girl Genius occurred about twenty years before the events of the comic, which resulted in chaos across Europa and Sparks fighting one another in the resulting havoc. It only ended when Baron Klaus Wulfenbach showed up and smacked all of the insane Sparks down to establish his empire.
 * Schlock Mercenary has the Terraforming War, in which both Tagons participated. Gradually some details were revealed.

Web Original

 * Red vs. Blue (especially the Recollection Trilogy) makes repeated references to some kind of great war against an alien race. The only details are that it took place during The Blood Gulch Chronicles and was resolved offscreen sometime between Blood Gulch and Reconstruction (or possibly sometime before the end of Blood Gulch), that Project Freelancer was one of many desperate initiatives towards the end of the war, and that humanity became allied with the aliens afterwards. The war occasionally seems to intrude on the Reds and Blues in Blood Gulch
 * Another possibility is that the war they mentioned is an attempt by Rooster Teeth to put the series into the Halo continuity. One example is the mention that the Freelancer-project was just one of the magic bullets created to win the war since the war was going really bad for the humans possibly referencing the different projects (for example Spartan II and III) during the covenant war. More can be read on the Red vs Blue WMG page
 * The My Little Pony: Friendship Is Magic spoof series Friendship Is Witchcraft features this in the second episode, "Read it and Sleep", with Rarity admitting that she is still traumatized after The War.
 * The "great war" eighty years before the opening of the show is frequently referenced in RWBY, and is responsible for some of the quirks and oddities of the setting. It had two of the four kingdoms on each side, and the losing side essentially wanted to quash all behavior -- like art, in particular -- which had a chance of producing negative emotions and thus attracting the Grimm.

Western Animation

 * Not exactly a war, but Avatar: The Last Airbender has the Fire Nation's destruction of the Air Nomads 100 years prior to the start of the series.
 * The War itself is an an interesting variation in the show. We know why it started (the Fire Nation needed resources), when it started (100 years previous), who is fighting it (Fire Nation vs Earth Kingdom and the mostly neutral Water Tribes), and the characters are fighting its final year. However, we only get, at most, a couple flashbacks over 61 episodes. We don't see any battles even during the present (well, three, maybe four if you count the drill), so no Alternate Universe Counterparts to Stalingrad for the Earth Kingdom (unless you want to count the, again mostly unseen, 600 Day Seige of Ba Sing Se by Iroh), or a Jutland for the Water Tribes, or even any D-Day recreations for the Fire Nation's first invasion of the Earth Kingdom at the start of the war. In fact, the entire century of conflict between Aang's freezing to when Katara frees him is mostly untouched even in fan fiction. Which is sad, because it has a lot of potential.
 * That may be mostly because it's a kids' show.
 * Which is a damn shame
 * According to Word of God, Adventure Time takes place after "The Mushroom War", which pretty much destroyed all of humanity.
 * Also notable is the war between rainicorns and dogs, which is never elaborated upon (beyond mention of Lady Rainicorn's father being saved by a dog at some point during it) but shown as a cause for great strife between the species.
 * Futurama occasionally makes reference to some war or another, usually for a quick gag. The one time one is relevant to the main plot is in "Three Hundred Big Boys", where the spoils from a recently-won Bug War are spread among the populace.
 * The war between the Autobots and the Decepticons in Transformers Animated. By the time the series starts, the war is over, with the Autobots having won and the Decepticons scattered to the far reaches of space.
 * The only flashback material was repurposed clips from The Transformers Generation One.
 * Speaking of Transformers Generation 1, it contains references to the Third and Fourth Great (or "Cybertronian") Wars, the assumption being that there were a first and second. (They're probably in the fourth one. Or the fifth, if you consider the ending of Transformers: The Movie to be the end of that particular war.)
 * The SpongeBob SquarePants episode of the Krusty Krabs video stated that Mr. Krabs created the restaurant some time "after the war".
 * One Kim Possible flashback showed Steve Barkin camping in the jungles with his comrades.
 * The Neosapien Rebellion a.k.a. the First Neosapien War fifty years ago in Exo Squad. It is particularly oft mentioned in the early episodes, before the Second Neosapien War breaks out and easily surpasses the original one in scope and impact.