Forever War

"Red Soldier #1: Do you know the meaning of this war? Red Soldier #2: Hmm? Red Soldier #1: I mean, what's the point? It can't be for the land because everything is burned, bombed, or polluted. It can't be for the money because there isn't anything left to spend it on. So what is it? Religion? Why do we fight? Red Soldier #2: To win the war. Red Soldier #1: Meh, works for me."

- Gone With the Blastwave

Two factions are fighting over... something. The original reason has either been completely forgotten or reduced to a historical footnote. They've been fighting for so long that no one can remember anything except the war. Sometimes, both sides will have an infinite supply of troops via some Applied Phlebotinum.

There are numerous reasons to have a Forever War, but in all cases the two sides cannot reconcile their differences for some reason. One side may exist simply to fight the other but despite their best efforts their foes remain indomitable. Perhaps one group simply enjoys fighting so much that they don't want to stop, or maybe there are political or economic advantages to constant warfare. Though the most common reason would be that the two factions had a reason to fight long ago and at this point the concept of peace is simply foreign to their culture.

If by some miracle one side does manage to win it usually isn't portrayed as a good thing. Questions like "And Then What?" might come up—they've become so used to war that they don't know what they will do now that there is no longer someone to fight.

May overlap with Hopeless War. For the science fiction novel which is not the trope namer, see The Forever War. Contrast Curb Stomp Battle.

Anime & Manga
""You mean the war's been over?" "For years.""
 * Gundam is something of a meta example. There are 11 TV series in it already and every one is built entirely around a war in different settings and characters. You'd think that the entire Gundam metaverse is in the state of perpetual war (especially true for the Universal Century). To go even further, the series almost always (with a couple notable exceptions such as Mobile Suit Gundam 00) compounds the reality that no matter how many times the heroes win the war, another will come eventually as if war is tied to humanity's existence.
 * The war between Earth and "Jovian Lizards" in Martian Successor Nadesico, which gets incredibly stupid and pointless once we learn why and how it started.
 * Macross/Robotech/etc.: Knowing nothing but war and aggression, most Zentraedi did not realize that there was another way of life. The Invid are aware of the cause of their war, but have lost their identity; their entire society is now reorganized for the sole purpose of revenge.
 * Brogy and Dorry, two giants on the One Piece island of Little Garden, have been fighting one another for one hundred years when the Straw Hats meet them. They casually admit to having forgotten the original reason (which of their hunted prey was bigger) and fight purely for the sake of honor.
 * The theoretical goal of the Last Battalion in Hellsing.
 * The Cannon Fodder short in Memories. In a walled city perpetually at war, everyone's lives and livelihood depend upon maintaining and firing the enormous cannons that make up most of the city. Nearly every building in the city is equipped with a cannon of varying size, able to fire huge artillery shells over the city walls. Though the story is centered around a young boy and his father, who works as a lowly cannon-loader, the film is dedicated to the lives of the anonymous citizens of the city who slave to fuel and maintain this parody of the twentieth century war machine.
 * Appleseed It is implied that Deunan thought she was fighting one of these before being brought to Olympus.


 * The war between The Federation and The Empire in Legend of Galactic Heroes is centuries old, and much older than any cast member alive at the beginning of the series. It's explained that it's spent a lot of that time being a cold war in stalemate, mostly involving border skirmishes.
 * And to further the trope, the only people who remember the reason of the war (workers fleeing an at-the-time oppressive state and refusing to come back) are historians.
 * Armored Trooper VOTOMS uses this trope as there was a century old war between Gilgamesh and Balarant, provoked by the presence of the Overman who are effectively immortal beings with Chirico being the most notable one.

Comic Books

 * In the Marvel Universe, two galaxy-level empires, The Kree and The Skrull, have been at war for approximately one million years. While the cause is known—The Skrulls offered to share their technology with the Kree if they passed a test, but when they failed, the Kree killed the Skrull envoys and stole the technology anyway—it doesn't matter anymore. Both races just wish the other dead, and in at least the Skrulls' case, their warlike tendencies have become hereditary (as in, in their genes).
 * The Kree of course because they are Space Nazis who kill anyone non-Kree for "polluting the gene pool" (despite the fact they are a genetic dead end)
 * The Kherubim/Deamonite War in the Image Universe has already lasted millions of years. Earth was a minor backwater of this war that lost contact, and the war kept going. When both sides finally re-established contact, they discover that the war had ended thousands of years ago but no-one told them. So they decided "to heck with them" and went on fighting anyway.
 * Rogue Trooper - in the Rogue continuity, the conflict on Nu Earth had a definite cause: the planet was situated next to a strategic wormhole, and the planet which controlled it would control the galaxy. In the Friday reboot, however, no particular cause was given, to further drive home the fact that that war sucks.
 * The Silver Surfer Requiem story includes an issue with two planets at war. Even before they invented space travel the two planets could communicate by radio. They spent generations building up their arsenals in anticipation of the invention of space travel that would allow them to wage war.
 * The endless was between Apokolips and New Genesis from the DC Universe has been going on since the beginning of time, and everyone seemed surprised when it abruptly ended.

Films
"Pierre LeClerc: Just like Vitalij said it would be, a war fought for so long, no one remembers why it started. Solid Snake: What's sad is that each time people think it'll be the last one, the decisive one."
 * Screamers: The two sides have all but obliterated each other and forgot to tell the characters in the movie.
 * Made even worse by the fact that the general they've been receiving orders from back on Earth is already dead.
 * Star Wars: How long have the Jedi and Sith been going at it? While the cause has not been forgotten (their basic philosophies require each to destroy they other, what with the Sith being a Religion of Evil and the embodiment of The Dark Side, and the Jedi...being the opposite of that), the origin presumably has.
 * Due to the supernatural elements, the war has been raging since before either group actually existed.
 * The thousand-year New Sith Wars definitely take the cake, though. Whoever was there to see it start wasn't there when it ended (obvious, considering most people's lifespans). A family could have participated in that war for roughly fifty generations if they were in it from start until finish. Even exceptionally long-lived aliens like Hutts and Yoda's unnamed species would've been unlikely to live long enough to see the entirety of the war.
 * And even not including the Jedi and Sith, war is still the most common event in the series - the Empire, even after Palpatine and Vader's deaths, kept on fighting the New Republic for decades. And then the Yuuzhan Vong came along.
 * Invoked in the Fan Film Metal Gear Solid: Philanthropy:


 * It's implied at the end of Vantage Point that this trope is the reason.

Literature

 * A major part of the Star Wars Expanded Universe novel Shatterpoint is the war that has been going on for ages between the Korunai native to Haruun Kal and the Balawai, or foreigners.
 * Likewise the war on Nim Drovis between the Drovians and Gopso'o (seen briefly in Planet of Twilight). The most common theory is that the war started with an argument over the meaning of the word "truth", but the combatants don't really care anymore; the war now contains elements of Feuding Families and Cycle of Revenge.
 * In The Hitchhiker's Guide to the Galaxy this happens due to Science Marches On within the story. Old slower than light ships are mentioned perpetually showing up and attacking their enemies centuries after the war is over and totally forgotten.
 * And when Time Travel was invented, It Got Worse. Battles started happening before the issues the war was will be about even arose. Will arise. Whatever.
 * The aliens in Pandora's Star exist as giant colony organisms who are basically immortal. Their "society," if you could call it that, does not recognize the concept of cooperation or coexistence. Each hive-mind has been at war with every other member of its species since prehistory. By the time the story takes place, the hive minds have settled into a stalemate between a dozen or so competing members. The interference of one incompetent human breaks the stalemate, with dire consequences for mankind.
 * In Gulliver's Travels Lilliput and Blefuscu have been fighting so long that they barely remember that it started over how to eat a boiled egg (Big Endians versus Little Endians).
 * In Hawksong by Amelia Atwater-Rhodes, the shapeshifting Avians and Serpiente have been entangled in a war that spanned over generations and has simply devolved into endless bloodshed.
 * Turns out, it was all engineered this way by the Falcons because the Serpiente originally contained and wielded the full power of a particular deity, Anhamirak. When the person acting as balancer for Anhamirak's powers fled, the Serpiente powers turned wild and destructive. The Falcons then split the Serpiente leader's power in half and gave the second half to a little girl, whom they turned into a hawk and thus created the Avians. Then both the Serpiente and Avian queens were assassinated with both sides blaming the other. Et voila, endless war that keeps both sides and their powers very separate.
 * A large part of the Thursday Next series of books is the hundred and fifty year old war between British and Russian forces over the Crimean Pennisula. Many important people believe giving it up would be a disservice to those who died on it. Few recognize the landmass is a bombed out hellhole worth nothing.
 * Joe Haldeman's The Forever War: Interstellar distances and miscommunications leads to thousands of years of warfare even more pointless than usual. Due to the Time Dilation caused by relativistic travel William Mandella (the narrator) survives the entire war, despite it lasting approximately 1143 years and Mandella going on fewer than half a dozen patrols.
 * "We are at war with Eurasia. We have always been at war with Eurasia."
 * "We have never been at war with Eurasia. We are at war with Eastasia. We have always been at war with Eastasia."
 * A straighter example is the constant crackdown on Goldstein and his supporters. O'Brien outright states to Winston that it will go on forever.
 * In Nineteen Eighty-Four, the Forever War is actually what makes the Dystopia of the book ticks in the first place. According to "The Theory And Practice Of Oligarchical Collectivism", it's possible for the regimes to create a wealthy, antiseptic scientific utopia (or a Brave New World) since they have the resources to create them in the first place, but that will cause hierarchical society, which is based on widespread repression, poverty, ignorance and blind faith to the Powers That Be, to fall apart. War has superseded its former meaning of conquest and has evolved into an excuse to waste resources, decrease living standards and create intense feelings of constant danger and fanaticism, feelings which have long been associated with loyalty to a group.
 * Fritz Leiber wrote a series of novellas and short stories about the Change War, a war of time travellers between "the Spiders" and "the Snakes." The two sides span galaxies and species as well as ages, and no one, at least no one the reader meets, knows what the war is about. Both sides are trying to redesign the history of the universe, but no one knows to what end, nor does the war appear to even have a history.
 * The war between Tsort and Ephebe on the Discworld. One can remember what caused it, and it only ever lets up when the thin country of Djelibeybi exists between them. Many notable wooden animals are used. Fitting its Troy parody nature, the cause is suggested to involve a beautiful (though not so much after twelve kids) lady and upset gods.
 * The Discworld also has the Battle(s) of Koom Valley, a recurring set of conflicts where dwarfs and trolls would wallop the hell out of each other, largely for reasons of tradition. The source of the conflict (your standard tragic miscommunication with a twist or two) was finally revealed in Thud!
 * The history monks didn't make it any better when they used it to patch a bunch of holes the first time the timeline was destroyed.
 * One of these also appears to be central to the events in Monstrous Regiment. Bonus points because it was a religious war, ordered by a Small God who has since been voted off the pantheon.
 * The war in The Lost Fleet has been going on for over a hundred years between the evenly matched Alliance and Syndicate Worlds. For the Alliance its a simple matter of "They attacked us first!" For the Syndics, well...  Not that they'll ever admit that.
 * In The Adventures of Huckleberry Finn, by Mark Twain, Huck gets caught up in a feud between the Grangerford and Sheperdson families. This is a new concept to him. His friend Buck Grangerford explains : "Well," says Buck, "a feud is this way: A man has a quarrel with another man, and kills him; then that other man's brother kills HIM; then the other brothers, on both sides, goes for one another; then the COUSINS chip in—and by and by everybody's killed off, and there ain't no more feud. But it's kind of slow, and takes a long time." "Has this one been going on long, Buck?" "Well, I should RECKON! It started thirty year ago, or som'ers along there. There was trouble 'bout something, and then a lawsuit to settle it; and the suit went agin one of the men, and so he up and shot the man that won the suit—which he would naturally do, of course. Anybody would." "What was the trouble about, Buck?—land?" "I reckon maybe—I don't know." "Well, who done the shooting? Was it a Grangerford or a Shepherdson?" "Laws, how do I know? It was so long ago." "Don't anybody know?" "Oh, yes, pa knows, I reckon, and some of the other old people; but they don't know now what the row was about in the first place."
 * Subverted in the most horrific way possible when
 * The Dragonriders of Pern present an interesting twist. Millennia have passed and the only real constant for the residents of Pern over that time has become that the Red Star will bring death from the sky. The thing is, it's only a war for one side—the "enemy" is a nearly non-living fungoid that literally just falls from the sky when the orbital mechanics are wrong. It could still wipe out most life on the planet if left unchecked.
 * The War against Morgoth and Sauron in JRR Tolkien's works. It does help that both the protagonists and antagonists contain immortal characters (Elves on the side of good, various wraiths, balrogs, dragons and other miscellanous creepy-crawlies on team evil).
 * The genocidal "Final War" between the Concordiat of Man and the Melconian Empire didn't end so much as peter out. After all was said and done, both sides ceased to exist as political entities, and what few surviving outposts of civilization remained either made peace with their neighbors or got exterminated by said neighbors.
 * In Life on Urth, there are two factions who have been fighting for years over that fact that somebody once at an appetiser that someone else wanted. After this went on for a few years, the soldiers' wives decided that the men should only have to fight from 9 to 5, Monday to Friday, and also get a lunch break. During the book, one of the protagonists ends the war by pointing out how silly the entire thing is. A little later, the guy stalking them gets the war started again when he explains how the entire country's economy was devoted to war, and without the fighting, everybody is going to be unemployed and stuck with unfarmable land.
 * Xeelee Sequence: The eponymous aliens have been fighting against their mortal enemies, the Photino Birds, for billions of years. Humanity's war with the Xeelee, lasting for mere millions, is inconsequential by comparison.
 * The war between the Confederation and the Others in the Confederation of Valor series has been going on for a couple hundred years by the time of book one.
 * In the Star Trek Terok Nor novels, part of what motivates Cardassian support for withdrawing from their Occupation of Bajor is the idea that, if the 50-year occupation goes on much longer, both sides will be too emotionally invested in it to ever stop.

Live-Action TV

 * Babylon 5 has the Shadows and the Vorlons, who have been fighting their war of Order Versus Chaos for millions of years. The Shadows ask everyone, "What do you want?", but don't know the answer to the question themselves any more. The Vorlons ask, "Who are you?", but likewise have forgotten their answer. When their respective noses are rubbed in this fact, they rather shamefacedly agree to leave the galaxy forever and let the younger races decide their own course between the poles of Order and Chaos for themselves. And then, a million years later, the Humans and Minbari evolve into First Ones and possibly start the whole damn thing over again...
 * It is hinted that the questions asked by the Minbari and the humans will be "Why are you here?" and "Where are you going?" respectively (the Minbari are deeply rooted in history and tradition, while the Earth Alliance are adventurous and forward-looking).
 * And there is every indication that Humans and Minbari have learned from the mistakes of the past and will head beyond the rim willingly once the younger races can get by on their own.
 * Doctor Who
 * The eternal war between the Sontarans and the Rutans, which gets mentioned each time one or other race appears in the series. It was stated to have been going on for 50,000 years as of The Poison Sky and was still going on in the serial The Sontaran Experiment which was set 20,000 years after that.
 * The long-running conflict between the Thals and the Kaleds on the planet Skaro. A conflict only brought to an end when an Omnicidal Maniac was placed in charge of peace negotiations. Which kinda started a whole bunch of new conflicts.
 * For that matter the Time War itself counts as both sides can travel through time causing it to be waged accross time itself, hence the name. The Time Lords even concluded that the only way to end the war would be to end time itself, which did not sit well with The Doctor. Additionally, Dalek/Time Lord hostilities and smaller skirmishes go back long before the war itself. Furthermore, since The Doctor and a number of Daleks managed to escape the time lock, which almost got broken once and might still cause the return of the time war, the surviving Daleks and The Doctor are still continuing the conflict.
 * The war between Atrios and Zeos in The Armageddon Factor. It eventually turns out that.
 * "The Doctor's Daughter". Since time immemorial, the two sides have been relentlessly cloning soldiers to keep the war going. The Reveal is that.
 * In the Star Trek: The Original Series episode "A Taste of Armageddon", two planets had been at war for centuries. They used computers to launch mathematical attacks and then order "casualties" to disintegration chambers. When Kirk posits that if they could come to an agreement on such a system, they should have been able to end the war, one planet's leader gives the fatalistic reply that they'd just start fighting again later over something else, so why bother with peace at all?
 * Also happens in the Star Trek: Deep Space Nine episode "Battle Lines" - casualties are resurrected by nanites at the beginning of each day.
 * A fate inflicted on them as a particularly terrible punishment: it's set up so they inflict hell on themselves. It's a self-perpetuating cycle, as each day they inflict more pain on each other and hate their enemy that much more. By the time of the episode, the hate has become so deep that even Star Fleet's famed speeches AND a Bajoran Kai can't get them to stop.
 * According to the leaders this was done to them because their constant fighting and refusal to make peace for generations had pissed off the rest of their race, which apparently liked ironic punishments.

Music
"Call connected through the NSA Complete transmission through the NSA Suspending your rights through the duration of the permanent war."
 * They Might Be Giants' free ringtone, "Call Connected Thru the NSA", invokes the trope against The War on Terror with the following lines:

Tabletop Games

 * Paranoia, where The Computer is at war with Commie mutant traitor spies, despite a lack of evidence for them. It's what it was programmed to do.
 * Dungeons & Dragons
 * Planescape features the Blood War, a battle between the Chaos-aligned Demons and Law-aligned Devils which had been raging pretty much since the beginning of existence and was expected to keep raging until the end... or so everyone else hoped, since it's generally accepted that if the two sides were to ever put aside their differences, everyone else would be royally screwed.
 * In 4e, shockingly enough, it actually did end, at least in the Forgotten Realms setting. There, Asmodeus managed to kill, and absorb the divine power of, a lesser god that literally fell right into his lap during the Spellplague. Using his new power, Asmodeus took advantage of the shifting planar cosmology caused by the Spellplague to forcibly "shove" the Abyss from its previous location to the bottom of the Elemental Chaos. While the Abyss and its inhabitants remain intact, there is no longer any easy way for demons to assault the Nine Hells in force from their new location.
 * The Valde Bellum in Nobilis has been going on for about two-thirds of the age of the universe (albeit, this only amounts to 4,000 years.) It will probably last to the end of all things... If only because that's the stakes.
 * The Intersteller Wars in Traveller. Also the fighting between the Third Imperium and the Zhodani.

Theatre

 * The Feuding Families of Romeo and Juliet had been fighting for so long that even the servants were involved and it seemed like no one really knew why they were fighting.
 * It's interesting to know that both the Montague and Capulet patriarchs seemed interested in bringing the war between their families to an end. If it hadn't been for that damned hot-headed Tybult ragging on the equally hot-headed Mercutio...

Video Games
""What began as a conflict over the transfer of consciousness from flesh to machines escalated into a war which has decimated a million worlds. The Core and the Arm have all but exhausted the resources of a galaxy in their struggle for domination. Both sides now crippled beyond repair, the remnants of their armies continue to battle on ravaged planets, their hatred fueled by over four thousand years of total war. This is a fight to the death. For each side, the only acceptable outcome is the complete elimination of the other.""
 * StarCraft: Maybe not so long in years, but sides switch so frequently that the original conflict is no longer relevant.
 * The plot of Total Annihilation was built on this trope. The only real survivors of the conflict are the military.
 * To quote the intro:


 * Its Spiritual Successor, Supreme Commander makes it clear that its galaxy is coming dangerously close to this state, especially during the Aeon campaign. They don't call it "The Infinite War" for nothing.
 * Actually, all the campaigns make it clear that the war is coming to a close.
 * The Aeon nearing victory is the driving force behind the sudden desperation in the other two campaigns. The Aeon campaign is all about preventing extremists within the Aeon from exterminating all other humans afterwords.
 * Xenogears, at least near the beginning, fits this quite well with the war between Kislev and Aveh. It gets twisted around like everything else later on, though.
 * Starlancer takes place in a hundred-years-long war between the Alliance (basically like Future NATO) and the Coalition (Future Warzaw Pact); the Alliance sending its last survivors elsewhere is what kick starts the plot of Freelancer.
 * Freelancer also has a backstory example with an 80-years war between Rhineland and the Kusari-allied Gas Miners Guild—one of the reasons why Rhineland is depicted as hostile to Kusari.
 * It's worth noting, however, that due to the futuristic setting and the increased life expectancies that come with technological advances that this is not exactly a straight example, as many would probably live throughout it and most would know why it started.
 * In Iji, The Tasen and  have apparently been fighting for thousands of years. While they still remember why, they seem to have trouble understanding what it would be like to not be at war.
 * In Breath of Fire 4, the conflict between the Fou Empire and the Alliance.
 * The war between the Terran Confederacy and the Kilrathi Empire portrayed in Wing Commander may not be all that old (it lasted from 2634 to 2669), but it fits the rest of this trope to a tee. By the time Wing Commander III rolls around, the war is older than pretty much all of your wingmen, and the only reason it looks like it could end any time soon is that the Kilrathi are very slowly gaining an upper hand.
 * The various nations of the Iron Grip series have been periodically fighting each other for entire centuries, if not millenia. War is almost an accepted way of life in this steampunky Crapsack World.
 * Iron Storm is set in a heavily dystopic Alternate History, where World War I never ended and has been raging on for 50 years, well into the 1960s.
 * World of Warcraft is Exactly What It Says on the Tin. The ongoing conflict between the two playable factions of the Horde (led by orcs) and the Alliance (led by humans) will not end. Despite numerous cataclysmic threats that are hostile to both sides, and numerous instances in the game of interfaction cooperation, there will always be skirmishes going on at the borders of the respective empires and the constant threat of more serious warfare heating up. Each side can point to several reasons for it, but at this point it's more about racial hatred and pervasive militarization than any good reason. (Well, that, and an excuse to earn Honor/Conquest points in PvP.)
 * Days of Ruin has Rubinelle and Lazuria, where both sides have fought each other for over a century. The Great War should have ended with the meteors, but even after civilization ends, the last surviving leaders on both sides (Admiral Greyfield and General Forsythe, respectively) refuse to end it. (It's more Greyfield's fault than Forsythe's.)
 * In the Assassin's Creed series, the covert war between the Assassins and the Templars has been raging since the dawn of human civilisation; unfortunately, it appears that the Templars are close to absolute victory.
 * Mystic Ark has a mostly-comedic version in the war between the Bloodhook and Gunboss. It's been going for centuries by the time the Player Character arrives, and none of the crew seem to have a reason for it besides that they've always been at war. Matoya outright states that none of them actually remember what the war was about anymore, and the captains can only manage an awkward silence when asked directly.
 * Justified in the case that they're both immortal, Kaguya Houraisan and Fujiwara no Mokou of Touhou Project have fought each other on a daily basis for several thousand years.
 * Order and Chaos in Shin Megami Tensei. Four separate realities and counting and they refuse to let up. Even though every human "fulcrum" they attempt to recruit to their sides has turned around and screwed both factions over (assuming Neutral endings, which seems to be the case), YHVH and Lucifer will never end things. Worse yet, Shin Megami Tensei Nocturne implies this has spawned a multiversal war used and abused by both sides with Humanity as their puppet in each possible universe.
 * Mass Effect: the Reaper cycle of extinction might not count (certainly it's been going on for a long, long time and was never meant to end), but their one-to-three-hundred-year exterminations do. Javik mentions it frequently—by the time he was born, the Citadel had already fallen and his world had been reduced to a blackened wasteland, and it only got worse from there.
 * The Rachni Wars deserve an honorable mention. They begin at roughly 1 AD, and the galaxy is on the back foot until the discovery and uplift of the krogan in 80 AD. It's not until 300 AD that the rachni were declared extinct.
 * Dark Souls is something of an odd example. While it isn't usually outright warfare, there has been a serious conflict between whether the Age of Fire should continue or end, a conflict which has been going on for at least 1,000 years.
 * Dark Souls is something of an odd example. While it isn't usually outright warfare, there has been a serious conflict between whether the Age of Fire should continue or end, a conflict which has been going on for at least 1,000 years.

Webcomics

 * Gone With the Blastwave. The first strip sums up the trope in a nutshell, as seen above.
 * Draconia Chronicles - The two races have been fighting each other for centuries and no longer remember the cause of the war. At this point the main reasons for fighting are vengeance and pride.
 * Erfworld operates by wargame-like rules and seems to be "a world where peace is impossible".
 * The only hope for peace is that the protagonist will wage a war so terrible it breaks war itself.
 * The Light and Dark Kingdoms in Homestuck are locked in a constant, unwinnable war until the arrival of Sburb players.
 * In Slightly Damned, the Angels and Demons are locked in an apparently divine-mandated war of annihilation, reinforced by numerous Remember the Alamo! incidents on both sides. The war is currently in a lull

Web Originals

 * After Republican France occupies Spain in the Chaos Timeline, the fighting down there does not end until eighty years later.
 * The Red and Blue Teams in Blood Gulch aren't really fighting so much as slacking off at opposite ends of the box canyon, and it only feels like they've been there forever, but if one's thing for sure it's that neither side has any clue why they're supposed to be fighting. They later travel to Battle Creek, where two teams of immortal zealots fight to Capture the Flag while spouting comments and insults straight out of X Box Live, and are revived at the end of each match, like a very stupid type of Valhalla.

Western Animation

 * Parodied in The Simpsons Halloween Episode. Marge convinces the alien robots to stop fighting only to have them join forces to enslave Springfield. Nice Job Breaking It, Hero.
 * The Transformers in various media. They may know what they're fighting for, but that doesn't change that they've been doing it for more than 4 million years. It's made even worse by the near immortality of Transformers. The same people have been fighting the same war for millions of years, and all over a planet that in some continuities is already doomed.
 * Avatar: The Last Airbender; Aang encountered two tribes who had been feuding for nearly a century. Details were sketchy after nearly a century, but each side claimed that the other side had wronged their emissary for no reason, thus setting off the feud. Aang (who was over 100 years old but spent most of those years as a Human Popsicle) then told the factions that the two "emissaries" were just children playing a game similar to Prisoner's Base, thus encouraging the two sides to iron out their differences.

Real Life

 * Ongoing hostilities between Israel and the Palestinians, which has been ongoing for approximately as long as there have been Israelis and Palestinians.
 * Though this is constantly cited as a real-life example, it would be generous to claim the Israeli-Palestinian conflict has cohesive roots older than 150 years.
 * The first official Arab-Israeli war started in 1967, less than 20 years after the founding of the State of Israel.
 * The Sunni-Shiite divide among Muslims. It started with a disagreement over the legitimate successor of Muhammad, who died in 650AD. Ali, whom the Shia back, was killed by his enemies in battle, and it went on from there.
 * The Hundred Years' War between England and France, which lasted 116 years (including some armistices). Given the average lifespans and literacy rates at that point, it's very likely most people had no idea what the war was about.
 * The Second Hundred Years' War (1688-1815) may also qualify, although the ideological backing for that conflict tended to be better known.
 * Persia's invasion of Greece was kind of like this... for the Persians. The Greeks knew exactly what they wanted out of it (that is, not to become a Persian province), but Xerxes wasn't entirely sure what he was doing there: Greece was a resource-poor and somewhat backwards excuse for a civilization, and the Greeks already in his empire (in Ionia, what is now western Turkey) had proven to be ungovernable. The only reason the Persians even thought about conquering mainland Greece was a peculiar battle in which an Athenian army assisted Miletos (a Greek city in Ionia) in reasserting its independence; in the process, they managed to torch the Persian provincial capital at Sardis. This made Xerxes' father Darius (who was Shah at the time) VERY angry once he got over his confusion (Athens was a tin-pot town nobody important had ever heard of). Darius shot an arrow into the sky, and swore "O God, grant that I may punish the Athenians;" later on, he had a servant remind him of his pledge at dinner daily, and various plans for fighting the Athenians were drawn up. Xerxes was not so preoccupied, and was rather confused with Darius' request that he also try to "punish the Athenians;" supposedly, the only thing that convinced Xerxes to go at all was a recurring dream of a phantom telling him to go to Greece.
 * Well, that's how Herodotus tells it. There's a recent interpretation that's gaining a lot of credibility that, since the Persian Empire was run on the Tarkin Doctrine, an Emperor had to be seen as living up to the exploits of his forefathers (remember, Xerxes is only the 4th Persian Emperor). This means conquest- and, for Darius and Xerxes, Greece is about the only thing left that's easy to conquer. Or at least they had every reason to expect it to be easy.
 * It also qualifies as "forever" because it raged on and off for about 160 years until Alexander the Great finally toppled the Persian Empire.
 * Heck, Alexander's conquest only put a brief pause to the conflict. One thousand years later, Greeks and Persians were still fighting each other.
 * See also the Arauco War, which started in 1536 and ended circa 1883. And some people want to start it back up again.
 * The Crusades started when the Byzantine Emperor began drumming up recruits in the West, and the Pope thought it a good way to get rid of unruly knights. Or they started when Muslim invasions triggered an on and off series of wars between Christians, and Muslims and-whoever. Or they are still going on. Or however. And yes, you are getting the idea.
 * Bizarre sort-of-well-not-really examples: Various wars have lasted a long time because people forgot the war was officially still going on. The Three Hundred and Thirty Five Years' War is notable for having no casualties, with no shots fired.
 * Inversion: The Anglo-Zanzibar war lasted somewhere between 33 and 45 minutes.
 * It's not a perfect example but the Thirty Years' War continued to be fought after the initial cause of the war had been resolved (mostly because it became a convenient excuse for other nations to advance their political goals.)
 * Conflict between the two Koreas has never officially ended and the two are technically still at war. Hostilities could recommence at any moment, but let's try not to think of what that might entail.
 * The Kashmir conflict between India and Pakistan has dragged on for decades, with each side holding contradictory positions and neither willing to compromise.
 * The conflict between the Sinhalese-dominated government Sri Lanka and the Tamil separatists seemed to be this, going on for 25 years with no apparent end in sight, until the Tamil Tigers were suddenly annihilated alongside alot of Tamil civilians in 2009.
 * The Cold War was expected to last forever until it suddenly ended in 1991.
 * The Vietnam War, part of the Cold War, lasted from 1955 to 1975 and was itself the continuation the war the French fought back when the area was called French Indochina... which was in turn a continuation of the war against the Japanese when they occupied French Indochina, which was in turn a continuation of the various conflicts in Indochina between the French and those seeking to evict them since the Annamese war... It goes on.
 * The War on Terror has no clear end and could potentially go on for decades.
 * Or at least until Terror is no longer a viable human emotion...
 * That is a snark, since what is meant is "war on terrorism" not war on an emotion and in any event that is a euphemism for "war on ghazis"(as there is no war on the IRA or the KKK or the Basque separatists in the news though there is one in practice) which is a fairly normal state in the history of Western Civilization and is familiar in the histories of Austria, Russia, Italy, The Balkans, and Britain just to name a few.
 * For large portions of history we didn't even bother to name our wars. War was the normal state of being except in the core of large states. In other words the only places where there was peace was where one faction had curb stomped everyone else in the area.
 * According to a UN statistic published in 2000 in the 100 years of the 20th Century there have been roughly 5 minutes of peace. The rest of the time there was a war being fought somewhere on Earth. Despite that, however, it was actually less violent than any previous century going by percentage of population lost.
 * Organized Crime and the police have what amounts to a permanent counterinsurgency in a number of cities. At least it looks like a counterinsurgency with espionage, hearts-and-minds operations and so forth. As the government has overwhelming force but is(sometimes)restrained by law and custom and the mob mainly wants to go about it's nefarious business the analogy only goes so far.
 * Similarly even in peacetime all nations are constantly engaged in espionage on each other.