Unspecified Apocalypse

"I have ideas [about the cause of the zombie plague]... but it's nothing set in stone because I never plan on writing it. So yes... I do know... kind of."

— Robert Kirkman on the origins of the zombie apocalypse in The Walking Dead

At some point in the past, the once grand (or seemingly grand) world was destroyed, and it was changed into what it is now. However, what exactly took out the old world isn't always known to the viewers (or even the characters!); it's either never discussed at all, or at best hinted out with a few details a sharp-eyed viewer or reader may see or read and be able to piece together. In a long series, it may be explained in bits and pieces (or, if the audience is lucky, completely) but, generally, there will still be many gaps.

Basically, we're talking about a very dark and extreme type of Noodle Incident.

Why this is done can vary. In some cases, this trope can help bring a sort of connection to the characters; After the End, information and knowledge is going to be lost or piecemeal at best, and when in a collapsed society death is ever-present, people are going to be more worried about day-to-day survival than times past. In other cases, the creators employ this trope since the cause of the fall simply isn't important, but rather, the world that comes after is the main focus.

However, as the series goes on, this trope can end up taking a backseat if the creators decide to expand a bit on the end, having this trope only count in the earlier parts of the work, and not in the later parts. This trope can also be downplayed; why the world ended may be known, but what caused the why may never be explained. For example, the audience may know that zombies or a nuclear war destroyed everything, but may not know why zombies came about in the first place, or why the war was even fought. And if they do find out, any information they'll get would be piecemeal.

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Examples

Anime & Manga

• Drifting Classroom revolves around a Tokyo elementary school that is somehow transported into a Bad Future where all of Japan, and presumably the rest of the world, is a desert wasteland inhabited by nothing except a sparse population of hideous mutants. According to the mutants, as well as an old film reel they have, this was caused by overpopulation, environmental damage and resource depletion, but not in any detail, and the source of the mutations is never explained, other than a vague story about humans just suddenly starting to give birth to them at some point. It's made even more confusing when it's revealed that a strange type of fungus that shows up after a flood begins turning any of the kids that eats it into the same kind of mutants.
• In Saikano, there's a war going on with an unspecified country or countries, also the world is dying for some reason, and it's actually destroyed in the ending. But no details are given.
• Sound of the Sky: 300 years ago, there was a great war that left humanity in shambles, but otherwise nobody really knows what happened. Most of the environment is uninhabitable, with the remaining population just trying to live in what few regions are still fertile.
• Yokohama Kaidashi Kikou: The story is set in a Flooded Future World where, for reasons that are never explained outside of hints and tidbits of information, some environmental shift has caused the oceans to encroach massively on the land, leaving humanity in a slow decline. The characters themselves don't ponder much in what caused the Age of the Calm Evening, and mainly deal with the effects it has on their lives. This is hinted to have been going on for years, and the main setting is a faraway settlement where such things are hardly talked about.

Comic Books

• During the original Kamandi run, the "Great Disaster" that devastated the world was explicitly stated to not be a nuclear war, but otherwise was never elaborated on. Later revisits to the setting retcon it to be a war after all, while Countdown to Final Crisis has it be a plague from the future.
• The reason for the vanishing of the heroes in Marvel 2099. Sometimes it's vaguely alluded that the heroes tried their best to save everyone, but failed. But never more than that, because by 2099, the age of heroes has faded into myth. The 2019 soft reboot is the first incarnation of the 2099 books to ever explicitly show what caused the world to become a dystopia: It's Doctor Doom's fault.
• The Walking Dead: A smaller example. We know that the dead walking again caused the end, but why it started happening is never really discussed. Word of God has even said that he has no plans to explore the reasons either. The one thing the audience can know for certain is that it wasnt an Alien Invasion, since Kirkman used this as part of the pitch to get the series picked up but never intended it to be the actual cause. This scenario was explored in the tongue-in-cheek (and extremely non-canon) Rick Grimes 2000 miniseries.
• Xenozoic Tales: In 2020, the Earth went batshit crazy with natural disasters and humanity was forced to hide away in great underground shelters. They re-emerge 450 years later, once everything has calmed down, to find a sort of Hollywood Prehistory world where prehistoric creatures of all eras roam through ancient cities that have been Reclaimed by Nature. How any of this happened is never revealed; speculation is made and hints are dropped (particularly regarding mysterious meteors containing something that causes havoc on evolution), but solid answers are few and far in between, and arguably just deepen the questions.
• In Y: The Last Man, it's never definitively revealed what caused the Gendercide that kills every male mammal on the planet (with a handful of exceptions). There are multiple theories purported, some clearly bunk, others somewhat plausible, none entirely satisfying. Word of God has it that one of them is correct, but refuses to say which.

Film — Animated

• 9: It is heavily implied some sort of war wiped out humanity, leaving our creations to inherit the Earth.
• Atlantis: The Lost Empire: Whatever exploded that caused the cataclysm that destroyed (most of) Atlantis and buried the part that was protected by the shield. All that is absolutely sure is that one Atlantean looks at another and yells out "You Fool! You destroyed us all!" before they both perish in the tidal wave that resulted from the explosion, but what did that will be forever unknown. Some dialogue later in the film strongly implies that it was something to do with the mysterious, probably-sentient source of their civilisation's Magitek reacting badly to being used as a weapon of mass destruction, but who the Atlanteans were at war with and why they weren't satisfied with their already-ridiculous technological edge over anyone else on Earth at the time is never explained, and the sequel film and spin-off series that might have gone on to do so never materialised.

Film — Live-Action

• The Book of Eli has a world decimated for an unknown reason (heavily implied to be nuclear warfare). A number of people who were alive at the time of "The Flash" still suffer burns, scars, and blindness from the event (including Eli).
• Children of Men: It is never revealed what caused the Sterility Plague that resulted in the Childless Dystopia and no-one seems to know what caused it in-universe as well. There are also quite a few mentions of Noodle Incidents in New York and Madrid that suggest that the rest of the world is being turned into nuclear wastelands or lawless war zones, especially if you believe the government propaganda.
• The Day: A group of survivors from an unexplained apocalypse roams the former US, trying to avoid the cannibal tribes that have sprung up in its wake. There's no discussion of what occurred, with the only thing clear being that society utterly collapsed, given the setting of the film.
• The Day After: While it's not completely unspecified (World War III erupting), there is one detail that is very specific, which various characters ask throughout the film for the sake of trying to feel better and that is deemed totally unimportant by the rest: who fired the nukes first, the Russians or the Americans? The reason within the film why the rest don't care is because the world is devastated either way and knowing this just won't fix anything. The reason in Real Life why this goes unmentioned is because the producers wanted to showcase the horrors of nuclear warfare and having the plot pointing fingers would be counter-productive — this is also the reason why the film was not Backed by the Pentagon.
• Hostile: The earth is a wasteland where mutants called “reapers” roam and few human survivors, is it left unanswered what caused the apocalypse beyond some vague implications it is connected to a terrorist chemical attack in New York.
• It Comes at Night: A mysterious, highly contagious virus of unknown origins led to the collapse of civilization. Supernatural entities may or may not be involved. That's about the extent of information we get about the apocalypse. The characters themselves aren't really sure what caused all this or whether said supernatural beings even exist. All that's clear is that society is gone, and they have to fight for survival.
• Logan's Run: What caused the end is never mentioned, in contrast to the novel, where overpopulation is stated as the cause for the dystopian society; more specifically, an Overpopulation Crisis that escalated until almost all of humanity was under 20 statistically. Once Population Control measures were instated, 20 became the maximum allowed lifespan. (30 in the movie).
• The world of Mad Max takes place in an anarchic society, where law and order is next to non-existent and ultra-violent gangs have risen up to rampage against decent people. Production documents state that the first movie takes place after a war between Saudi Arabia and Iran, which led to an oil shortage. But what happened between the first movie and Mad Max 2: The Road Warrior? Things got worse. It is never really explained how the world got to this horrific state, but in the video game, Max basically says that — as far as he can tell — literally everything that could go wrong did go wrong, all at once, and consequently nobody really knows which specific catastrophe actually caused the apocalypse; the collapse of society, massive wars destroying countries, oceans drying up, super-plagues everywhere, and more.
• Pandorum starts with a Sleeper Starship called the Elysium travelling towards a distant planet for colonisation when they receive a message from Earth saying that they are all that remains of the human race. Following flashbacks mention that the Elysium tried to contact and then find Earth, but it had been completely vaporised somehow, and no theory is of help at the current moment in the story.
• Planet of the Apes: The details involving the nuclear war in the original series are never explored. All that matters is that the apes inherited the world.
• The Postman: There are some hints of what happened, but it is never made clear exactly what.
  • General Bethlehem claims to have been at "the Battle of Georgetown" and seen the White House burn to the ground.
  • In the opening sequence, the old news reports playing in the background have what are clearly missiles going off. A nuclear exchange can therefore be inferred to have happened, which explains the "three-year [i.e. nuclear] winter" and why no one goes near major cities (likely destroyed and irradiated).
  • The old letter that Shakespeare delivers talks about strange weather, food shortages and a soldier returning home because the war was already over by the time he got there.
  • The events which brought the world to this are varied and unexplained, with events like "the war", "the rains" and "the bad mumps".^note The "bad mumps" is nothing more than having them as an adult, when they are almost lethal and often render males infertile, just like with Abby's husband, although she says he had them "as a boy". It's also mentioned that one catastrophe was "the Bugs". "Bug" being a slang for illnesses, it's not inconceivable that some of the WMDs exchanged were biological rather than nuclear. These "bad mumps" thus might have been a version designed to affect people more that he lived through.
• Shaun of the Dead: There are multiple reasons given for the Zombie Apocalypse, including a new super-flu, GM food, radiation from a downed satellite in reference to Night of the Living Dead (1968) and it is intentionally vague to which one is the true cause. In the denouement, a news anchor starts saying that scientists have now determined the cause to be... and is cut off when someone changes the channel.
• Stake Land involves a vampire apocalypse devastating North America (and the rest of the world including the Middle East, except apparently for the northern-most parts of Canada) and two men heading towards this "New Eden". There is never any specific information about where the vampires came from or how they came to exist.
• Warm Bodies: R mentions a couple of possible reasons the zombie plague happened, then admits he isn't sure which if any is true and concludes it doesn't really matter.

Literature

• In After Man: A Zoology of the Future, little detail is given on how, exactly, humans became extinct. There is some vague suggestion that it had something to do with overpopulation and resource depletion, but nothing more than that. This is because the focus of the book is an exploration of natural selection and animal evolution, and as the impact of humanity on the environment would make things too messy to easily predict mankind is handwaved as having died out so as to avoid having these issues take over the setting.
• Bas-Lag Cycle: The khepri fled their native continent en masse to escape a disaster known as "the Ravening". Whatever it was, it traumatized their kind so completely that none of the survivors of their 25-year sea journey to Bas-Lag ever passed on the details of the catastrophe, or of the ancient khepri culture it destroyed, to their descendants.
• The City and the Dungeon is set long After the End, but nobody seems to know what that end actually was. Some kind of apocalypse destroyed all the major cities except the City where the story is set, and it seems to have happened just before or right around the time the Dungeon was discovered, but that’s about the extent of what anyone's learned. Whatever happened must’ve been pretty terrifying; mention is made of how the ruins of destroyed cities are covered in massive claw marks, as if they were ripped apart by giant monsters.
• City of Bones (1995) is set a thousand years after a calamity that reduced most of the known world to a Thirsty Desert. The few remaining historic records are from the "Survivor" era when the Waste was new (and molten). Subverted late in the book, where a new find reveals that the Waste was a side effect of Ancient humanity's desperate attempt to hold off an invasion of malevolent spirits from Another Dimension.
• The Day of the Triffids:
  • Downplayed. It's clear how civilization collapsed — mysterious green flashes drove nearly everyone in the world blind — but the nature and origin of these things isn't clear. They're alleged to be caused by a malfunctioning Kill Sat, but this is explicitly nothing more than an educated guess on the protagonist's part.
  • The origin of the Triffids themselves is equally unknown — they simply started growing all over the Earth one day. The theory put forward in the book is that they were engineered by the Soviets, then spread when a plane attempting to smuggle samples to the USA disintegrated at altitude, allowing the wind to spread seeds everywhere. However, this is based on the claims of a single, now dead, person and is again presented as nothing more than a best guess by the narrator.
  • The 1962 movie explains away both of the above items to a meteor shower and an explicitly alien plant. Whether or not this counts as Adaptation Decay is left to the specific audience member — they are far from being the only changes done in the adaptation.
• Something happened in the distant past of The Dinosaur Lords that caused the ancient, advanced human society inhabiting Paradise to collapse and regress technologically. Ruins and technology of their time is scattered across the land. It’s never revealed what exactly happened, though hints are dropped that the Gray Angels were involved.
• In Dreamsnake, while it's clear it was some sort of nuclear war from the radioactive craters still dotting the landscape, who was fighting and why has been lost to history.
• The Future is Wild: In the original BBC version, humans go extinct for an unspecified reason at some point before five million years in the future. The American version changes it so they simply left Earth and colonized a new planet. Either way, this lets the work ignore the continuing impact and development of human civilization to focus on the evolution of wildlife and ecosystems.
• The Giver Quartet: Gathering Blue mentions The Ruin, a recurring event throughout history that has brought humanity to its knees again and again. The last time it happened, it is implied to have been to modern civilization. While the settings of Gathering and Messenger and the village that takes in Claire in Son have regressed to medieval level tech (with a few smackings of Schizo Tech and Lost Technology here and there), The Giver (and a few briefly mentioned, but never explored societies) managed to end up with futuristic technology. There is an unspecified society that owns the boats that deliver supplies to the Community that is at least at industrial level, that apparently didn't dip into Sameness, but the series never goes into details about it.
• The Hands of the Emperor: The Fall of Astandalas, between 25 and a thousand years back: Readers never learn exactly what happened and what caused it, and even in-universe, the knowledge is iffy: whatever happened broke the empire that had endured for around a hundred generations, brought disaster, famine, death, even falling lands and the disruption of weather, magic and time itself.
• In The Hitchhiker's Guide to the Galaxy, Ford Prefect is said to be the son of the only survivor of the Collapsing Hrung Disaster on Betelgeuse VII. His father was never able to satisfactorily explain what a "hrung" is, why it had collapsed (or why it chose that planet to do it on), or how he's survived it himself.
• Humanity Has Declined: The human race is slowly dying out; exactly why is never spelled out, and the humans seem no worse than melancholy about the notion.
• The Hunger Games: The event that caused the fall of this world and the rise of Panem is never stated. It is hinted to be some sort of environmental catastrophe though. Whatever it was, for whatever reason, one consequence is that planes have to fly low to the ground, since the upper atmosphere is apparently non-existent.
• Malevil has the characters trying to survive in the post-World War III, nuclear warfare-inflicted chaos that assails the French countryside. At no point it is ever found out what triggered the nuclear exchange-whether it was a type of Failsafe Failure, flat-out war or insane General Ripper-types on both sides pushing the button, the characters speculate a lot but finally agree that this a question that will probably never be answered and holds no importance in light of their current plight.
• Played with in The Peripheral. One half of the story takes place in the future, after "The Jackpot" wiped out a large chunk of humanity, with the survivors — largely rich folks — rebuilding after. A character in the present asks what "The Jackpot" was, and her future contact person eventually explains that it wasn't a singular apocalyptic event so much as various economic, environmental and sociopolitical trends and smaller events (the assassination of the U.S. president, for example) over the course of several decades of decline.
• The Precipice: The nature and origin of superpowers is not clear, and the most likely source is a massive meteor storm that happened in the 1960s, resulting in a massive worldwide famine and millions dead.
• The Road: What brought upon the end of the world is never really stated; theories ranging from asteroid impact to a nuclear war have been brought to the front. Whatever it was, it is of little consequence to the characters, who will be dead anyways at some point as the biosphere is now dead.
  The clocks stopped at 1:17. A long shear of light and then a series of low concussions.
• In Sime Gen, the fall of "our" civilization was caused by the mutation that split humanity into the titular Simes and Gens, but what caused the mutation to occur in the first place has no definitive explanation and, according to the authors, will never have a definitive canon explanation, though in character speculation is fair game.
• Sunday Without God: The legends say that God abandoned the world fifteen years prior, and as a result no one can truly die or give birth. Other characters doubt this story, believing instead that one day, everyone became a Reality Warper and collectively wished to live forever, thus distorting the nature of death. Whatever the reason for why the world is slowly coming to a standstill, the characters have to deal with the lack of true death and the consequences of people's deepest wishes coming true.
• In An Unkindness of Ghosts, humanity has gone extinct except for the inhabitants of a Generation Ship. We never learn what happened, especially since plant life and at least some animal life has survived.
• Cory Doctorow's short story (eventually turned into a comic) "When Sysadmins Ruled the Earth" describes an unspecified apocalypse from the viewpoint of a system administrator, who has to go to work late at night due to a server issue. While there, he gets a call from his wife, who tells him that their infant child has already died from an unspecified cause, and she herself dies while on the phone. Very quickly, the sysadmins lose contact with the rest of the world. Eventually, they manage to re-establish contact with others like them via the still-working Internet and establish an Internet-based government. Word of God is that this trope is invoked deliberately, since a regular person is highly unlikely to know the details of a sudden apocalypse and likely wouldn't care anyway. They get an email - purportedly forwarded from Health Canada — that the whole city’s quarantined because of a biological weapon, but as everything falls apart very quickly, it's never confirmed.
• The Witch of Knightcharm: One of the new recruits at an evil Wizarding School is Janet Yawkly, an Anabaptist who hates violence and clearly is terrified of everything around her. This raises the question in the protagonist's mind of why Yawkly is there in the first place, and while she doesn't say exactly why, it's implied (through her strict use of the past tense when referencing her community) that something horrible happened and destroyed them.

Live-Action TV

• The 4400: The exact nature of the catastrophe that causes the near extinction of humanity in the future is never revealed. If a reveal was in the plans, we just never got to see it.
• In Firefly, vague allusions are made to Earth That Was, implying that something cataclysmic happened to cause an exodus. Details are absent. The most explanation we're ever given is one version of the show's opening, which simply says that Earth got "used up," and the prologue to the film Serenity, in which a teacher says Earth could no longer sustain its population.
• The Flipside of Dominick Hide has some sort of apocalypse at the end of the 20th century which left most of the planet contaminated with pollution and poison, but it isn't specific as to what did it.
• Enforced in the Life After People film and series, as it's explicitly stated to be the story of what's left behind after humanity vanishes, not why/how we disappear.
• The Lord of the Rings: The Rings of Power: The destruction of Beleriand is never referred, just vaguely shown for a brief in Galadriel's monologue for legal reasons.
• A recurring That Mitchell and Webb Look sketch later in the run known as "The Quiz Broadcast" takes place after an apocalypse referred to as "The Event" (remain indoors). Exactly what the Event was in unclear, but mention is made of extreme levels of radiation, and all the children dying in the aftermath. Not to mention Them, an unidentified infectious disease, and the complete and total loss of near-all human knowledge.
  Host: Multiple choice: Which of Shakespeare's three plays is now thought to be prophetic of the Event? Is it A) Pericles, B) Cymbeline, or C) Boeing-Boeing?
  Sheila: [buzzes in] Is it a trick question?
  Host: It is.
  Sheila: [screams and runs out of the room]
  Host: Oh dear, oh dear, some horrible memory from The Event, no doubt.
  Peter: We all get them.
  Host: Yes indeed; by night, we all get them. Please, everyone, remain indoors.

Tabletop Games

• Base Raiders takes place in a superhero universe Earth where an event simply known as "Ragnarok" made all of the superheroes and supervillains of the planet simply disappear overnight. It must have been something of insane proportions for this to happen, but if there is anybody on the planet who knows the specifics, they ain't telling. The only thing the player characters care about if that this has left a myriad of secret bases full of comic-book superscience and magic gear lying around ready to be plundered and sold on the black market, justifying the game's angle of "modern-day Dungeon Crawling".
• Dead Reign takes place in a worldwide Zombie Apocalypse that was caused by a strange sickness known only as "The Wave" which killed people and made them rise as zombies. What actually caused the wave in the first place is unknown with most survivors not really caring about finding out what happened in favor of trying to survive for another day.
• Gamma World: The events that destroyed the world are different from version to version, but for most versions the details remain in the dark.
• Numenera takes plane in "the Ninth World", Earth a billion-plus years in the future after civilization has risen and fallen multiple times, leaving behind a whole lot of weird gadgets (the titular Numenera) and ruins. Not only does nobody knows how any of the previous Worlds fell, nobody is even sure if there were only eight Worlds prior to the "current day".
• Paranoia takes place after something only referred to as the Big Whoops. But, whatever happened, Friend Computer is sure it was caused by evil Communists. Some of the Ultraviolet sections reveal that an asteroid the size of Sheboygan made its way to Earth, causing the Big Whoops. A Russian missile silo mistook the asteroid for a nuclear attack, and The Computer mistook that counter-nuclear attack as an attack by Communists (its information records were damaged, and it could only retrieve 1950's cold war propaganda at the time). They then tell the Gamemaster to use this explanation, come up with another one, or keep changing the backstory, all to keep the players experiencing the setting's trademark Fear and Ignorance.
• Rifts (by the same company that makes Dead Reign) is set roughly 300 years after an event called "The Great Cataclysm" or "The Coming of the Rifts" nearly destroyed humanity, and reshaped the world. What's mainly known to people living on Rifts Earth is that political tensions were rising at the time, and it's assumed that some kind of war broke out, though how that lead to the Coming of the Rifts is unknown. Bits and pieces were teased out in the books for years. At present, most of the story is known. The Great Cataclysm was triggered by one South American nation nuking another South American nation on the Winter Solstice at midnight, during a rare planetary alignment. This combination of events, millions of people simultaneously dying when the Earth's magic level was higher than it had been in millennia, caused a chain reaction that nearly destroyed the world. Details are still left out, such as which nation bombed which other nation, and why. But since the cause of the Cataclysm isn't the focus of the game, we'll probably never learn all details.
• Warhammer 40,000 used to have a lot of these, with human civilization having collapsed several times in its history both before and after colonizing the galaxy. Most of these have since been explained in various books and other bits of lore added over the years. However, in-universe they're still almost all mysteries, if people even know they happened at all.

Video Games

• After the End: A Post-Apocalyptic America takes place centuries after the world underwent some sort of cataclysm, with humanity having managed to work its way back up to medieval society and technology. The exact nature of The Event is deliberately left vague and up to the player's interpretation.
• Beware: The world you traverse is a desolate, muddy ruin filled with car wrecks and cow skeletons, and the only other living beings you encounter there are either people who don't trust you enough to speak to you or things out to kill you. It's possible to reactivate an old projector showing an endless traffic jam and news slogans referring to a famine and blackout that apparently overwhelmend the government and led to the infrastructure collapsing. However, what caused them, how far they extend and how they're connected to the aforementioned Humanoid Abominations now stalking the land is unknown.
• Civilization:
  • The Final Frontier mod for Civilization IV has all contact with Earth lost, and the game outright states at the beginning that it is likely that something terrible happened to it. Dialogue in tech quotes hint that Earth was trying to do some sort of transcendence project that went wrong, and destroyed the entire star system.
  • While the world isn't destroyed in Civilization: Beyond Earth, it's in bad shape after something called the Great Mistake. Word of God is deliberately mum on what the Great Mistake was. All we see in images and trailers is widespread poverty and the flooded Pyramids. Some additional material indicates that natural resources are close to being used up, which is why the Seeding missions to other worlds are financed in the first place. The Purity and Supremacy victory conditions involve building a gate to Earth. The Purity-aligned faction strives to build the Exodus Gate, which has refugees from Earth pouring in, requiring them to be settled somewhere. The Supremacy-aligned faction attempts to build the Emancipation Gate (looks pretty much the same), and then sends troops to Earth to engage in some Unwilling Roboticisation.
• Death Road to Canada takes place during the zombie apocalypse, where all other nations have fallen except Canada. No reason is ever given as to how or why it happened, as the only goal of the survivors is to drive from Florida to Canada.
• Destiny takes place in the aftermath of the Collapse that ended human civilization, leaving ruins strewn across the solar system and the survivors gathered into the Last City on Earth. For the longest time, what actually happened in the Collapse was a mystery, as was the exact nature of the Darkness said to have caused it. Details about both were slowly revealed across the game's lifespan and its sequel's; ultimately, a lore book in Destiny 2 mentioned without much fanfare that it mostly involved the Darkness barraging every world with natural disasters, too many to respond to or recover from.
• Dragon Age:
  • Dragon Age: Origins isn't quite After the End, but the origin of the Darkspawn who pour out in hordes to kill everyone from time to time are not truly known. The dominant religion claims they were created when a group of powerful mages broke into the Creator's city and were cursed for doing so, but the game makes it clear that no-one really knows and suggests this may just be a fable warning about the hubris of humanity.
  • Dragon Age: Inquisition's main antagonist claims to be one of those mages which may support the legend being true, but it's still never shown that he's actually telling the truth, and the apparent involvement of gods from other pantheons suggests that at the least there's more to the story than that.
• The Elder Scrolls:
  • In a race-specific example, the series has the (believed to be) extinct Dwemer, the "Deep Elves" or "Dwarves", of all of North Tamriel, whose civilization ("Dwemereth") once spanned from Hammerfell across Skyrim to Morrowind, where the epicenter of their culture was built in and around Red Mountain. They were a highly technologically advanced race who created all manner of Magitek and Steampunk technology, which remains unmatched by any other race in Tamriel. They were also extreme Naytheists for whom a major part of their outlook was the idea of refuting everything as real. During the mid-1st Era, they discovered the Heart of Lorkhan (the "divine center" of the dead creator god of the mortal plane) deep beneath Red Mountain. Though there are many different versions of the story regarding what happened next, the Dwemer did something with the Heart that caused their entire race to disappear from every known plane of existence in a single instant. The leading theory (which you can put together yourself in the Mages Guild quest line in Morrowind) states that they were trying to break themselves down into their base elements before ascending into divine form. However, they got something wrong with the "reforging" step and instead blinked out of existence. Other theories state that they may have even been successful in their attempt, and are currently on said "higher plane." Making it only more confusing is one particular Dwemer ruin that shows whatever happened was violent and abrupt: it's a residential area, and you find piles of ash that used to be Dwemer in beds or near their piles of equipment on guard duty. Despite the theories, no definitive answer has been given in the series to date. One single Dwemer, Yagrum Bagarn, was off exploring unsubscribed "outer realms" at the time and returned to find his people gone. He doesn't know what happened either, or why he (and apparently only he) remained, and he only lived to tell his tale because he became infected with the Corprus Disease (one of the side-effects of which turns the sufferer into The Ageless). The In-Universe mystery of the Dwemer has only deepened by the time of Skyrim since much of what was known about the Dwemer was again lost in the 200 years following the Oblivion Crisis and the eruption of Red Mountain (which wiped away a great number of Dwemeri ruins in Vvardenfell, the epicenter of Dwemer culture prior to their disappearance). Even one of the greatest experts on the Dwemer, Calcelmo, knows less about the Dwemer than some amateur archeologists in Vvardenfell during the time of Morrowind. Arniel Gane of the College of Winterhold tried to use an Dwemer dagger called Keening (the one used on the Heart of Lorkhan) and a warped soul gem to perform the ritual the Dwemer Tonal Architect Lord Kagrenac did on a much smaller scale... and he did it alright. After his quest, the Dragonborn can summon his shade from where ever he is now.
  • The Great Collapse mentioned in Skyrim. In 4E 122, the Sea of Ghosts destroyed almost all of the city of Winterhold save for the Jarl's longhouse, a few surrounding houses, and the College of Winterhold (allegedly protected by magical means). Nobody knows why it happened but the citizenry believe that either the College caused it or at least could have lessened the damage while the College believe it was caused by the destruction of Vivec and eruption of the Red Mountain causing tsunamis and destroying the majority of the area. Regardless Winterhold is a shell of its former self.
• Enslaved: Odyssey to the West takes place After the End, in the ruins of the modern times. What exactly happened to nearly wipe out humanity is never even discussed; characters mostly focus on continuing their survival and barely question the relics of the past.
• The nature of the apocalypse in Fallout is obvious and widely known; a global thermonuclear war. However, nobody seems to know how that fateful nuclear exchange started, nor who fired the first shot that kicked it all off. The world was already in a pretty tense state, with the US having just come out on top in a brutal war with China and most of Europe collapsing into quarreling nation-states, so there are plenty of suspects, but no one particularly cares about finding out who shot first; few are concerned with such historical information when they are fighting for survival every day.
• The world of Fate/EXTRA is quite different from the real world or the world as it exists in most other Nasuverse stories: something happened in the 1970s that led to a great disaster and resulted in all magical energy in the world vanishing, never to come back. What form this disaster took, and what the immediate consequences of it were, are all unknown. All that is known is that it was a global catastrophe that altered the course of human civilization. Word of God states that the root cause was a group of vampires attempting to perform the Aylesbury Ritual to awaken the Dark Six (a kind of vampiric messiah figure) and failing terribly at it, but beyond that any details are unknown.
• Hyper Light Drifter: The world is littered with the ruins of a past civilization that was destroyed after the arrival of the Titans, whose corpses are scattered throughout the land. Just what exactly happened is unknown, and none of the characters show any particular interest in finding out; as far as they know or care, the world's always been like it is. Some hints are dropped that the species your character belongs to may have been responsible, or at least played a part in it.
• The nature of the apocalypse in I Am Alive is left vague, only that most of the world is now covered in toxic dust and human civilization has collapsed.
• LISA: There was an apocalypse event called "The Great White Flash" that eliminated all women. And that's all we know. We don't know what it was, what caused it, what it actually did to the women, or if the After the End setting was directly due to the Flash or if society simply collapsed due to half the population vanishing.
• All we know about the reason of the apocalypse in The Long Dark is that electricity ceased to function due to some electromagnetic storm.
• A recurring apocalypse of unknown cause is central to the background of Mass Effect. Discovering the truth and then actually convincing other people of it forms a large part of the first two games.
• Metro: What caused the war of 2013? The official website shows that the initial nuclear explosions were in the Middle East and the situation then escalated. Beyond this, all we know is that it was probably between Russia and NATO, but even that is unconfirmed. To the residents of the Metro though, figuring out the facts hardly matter.
• A Mind Forever Voyaging: The world in 2081 is portrayed as a post-apocalyptic ruin filled with barbaric gangs and feral dogs. It's never explained just how civilization collapsed; the player character has no memory of the event and the surviving humans aren't exactly keen to enlighten you. Given the multiple environmental and political crises plaguing the world in 2071, it's highly likely that there was more than one cause.
• Nier: The game is suggested to take place in the far future, but what exactly wrecked mankind's civilization isn't well-explained. There's talk of a great "Dragon" and "Giant" suddenly appearing in a city, fighting each other, and then getting killed shortly afterward, and then something called "White Chlorination Syndrome" spreading across the planet, but the details are left vague... at least, in the game itself. Supplementary materials contain extensive timelines and details about what exactly happened and how it lead to the state of the world in Nier.
• The only thing known about the apocalypse in Nuclear Throne is that it was caused by nukes, heavily irradiating the world and its inhabitants, creating a barren wasteland in its wake.
• In Obduction, there's a theory among some of the characters that the alien seedpods that randomly abduct people to a strange planet are doing so in order to preserve the human species against some unknown but imminent cataclysm. They are correct, as seen in the bad ending (and one specific vantage point in a late-game area): we don't know what went wrong, but it's apparent that Earth got messed up, as there are scorch marks, ruins, and massive dust clouds roaming the surface.
• Exactly what happened to Earth in Outriders isn't elaborated on. It's treated as a analogy for global warming caused by human excess, but it's also mentioned the planet was ultimately destroyed by earthquakes which all the pollution and energy-guzzling appliances in the world isn't going to cause.
• Path of Exile: The Vaal civilization. Their last leader, Queen Atziri, was obsessed with preserving her beauty, and when she discovered a recently dead serial killer supposedly lived to be 168 years old yet looked youthful, she tried to find how he accomplished that, by any means necessary. Human Sacrifice was already a common practice for the Vaal, but Atziri took it to a new level, since the rumor was that he stole the youth of his victims somehow. One day, her thaumaturgist Doryani did some kind of ritual, and the entire civilization collapsed instantly. Only a handful of 3000 or so refugees survived the fall. The only thing that remains from the Vaal are ancient ruins, a Sealed Evil in a Can with the souls of the fallen, and a corrupted dimension controlled by Atziri.
• Rimworld: The world you're trying to survive on once supported a civilisation advanced enough to leave behind the crumbling remains of highways and an occasional vault full of Human Popsicles, not to mention all the "compacted steel" and "compacted machinery" for your settlers to dig out of the ground and repurpose, but what precisely caused it to fall is never explained.
• Whatever destroys the Earth in Seedship is never explained. It's very likely that whatever it was also took out the solar system as well, as text in the game refers to Earth's star as "dead". Seeing that the titular ship does have the ability to create successful colonies on non-habitable worlds, which the solar system has plenty of, this is likely the case.
• The timeline of the Starsiege trilogy actually starts with an unexplained apocalypse laying waste to the world and bringing humanity to the brink of extinction before bouncing back After the End. Interestingly, no one knows what happened or what the calamity even was; some speculate nuclear war, others think it was a pandemic, and at least one sect argues that the Rapture came and went and the remaining humans the leftover rejected sinners. If Dynamix's canon is to be believed, aliens were involved somehow. This apocalyptic event is simply known The Devastation. Humanity undergoes a very specified Robot War as their second apocalypse, known as The Fire.
• World of Warcraft: The Apexis civilization which once dominated Draenor was wiped out in some unknown cataclysm. Chronicles does eventually reveal that a civil war ended with the detonation of a Fantastic Nuke which nearly wiped out the arakkoa and destroyed all records of what happened.

Visual Novels

• Danganronpa: In the last trial of the first game, the Mastermind (a.k.a. Junko Enoshima) reveals that the reason the students weren't actually trapped, but instead choose to stay inside the school for the rest of their lives was because of "The Worst, Most Despair-inducing Event in the History of Mankind" that caused the downfall of society. However, the specifics of the Tragedy aren't shown until the second game.

Webcomics

• Sarilho: Something happened to the modern world, but the details aren't shown. Judging by the maps, this was either accompanied/caused by a raise in the sea levels.

Web Original

• In Gold Tongues, it's heavily implied that most of civilization has perished due to an unknown virus, along with thousands of ravenous, man-sized bugs having preyed on human beings. How the bugs arrived in the world and the kind of virus that broke out and killed most of humanity is never revealed.

Western Animation

• Adventure Time: The Great Mushroom War is the reason behind the formation of the Land of Ooo, but for the longest time, the fact that the world was even After the End was just hinted at. Even by the end of the show, the details — who was fighting whom, the exact nature of the weapons used, how or whether it's connected to the rise of magic, etc. — are never entirely revealed, though enough hints are dropped for you to piece together a vague idea of what happened.
• American Dad!: The episode "The Two Hundred" begins with a grizzled and tattooed Stan returning to a ruined Langley Falls in search of his missing family, and the only thing we find out is that something called "The Wave" destroyed the world and wiped out most of humanity, with the few survivors being driven to cannibalism to survive. It's not until the last few minutes that it's revealed that the global apocalypse was caused by Roger accidentally being trapped inside a particle accelerator, which combined with his Bizarre Alien Biology to create a World-Wrecking Wave that swept across the planet, reducing it to ashes. It also led to an army of Roger copies, each one being one of his personas, popping into existance.
• Kipo and the Age of Wonderbeasts: Whatever event occurred in October 2020 that resulted in planetary and societal disruption, the appearance of huge or otherwise mutated, sapient animals, and forced the remainder of humanity to either live in sheltered underground communities or as lone survivors on the surface is unknown.
• Love, Death & Robots: In "Three Robots", there are conflicting reports as to why humanity went extinct. A nuclear holocaust is proposed first, and 11-45-G's research suggests it was environmental catastrophe brought about by environmental degradation and climate change. The cats claim they did it because humanity had ceased to be of any use to them once they were given thumbs, but this isn't reliable when the same cats are trying to take the robots hostage by exploiting their ignorance. The only thing the follow-up episode "Three Robots: Exit Strategies" focuses on is showing (and mocking) how the rich and connected tried to survive and failed.
• Motorcity: The world outside of Detroit is said to be an uninhabitable wasteland, but how it got that way is unknown. In fact, the characters aren't entirely sure there even was an apocalypse; nobody has ever actually seen outside the city and in one episode, the arrival of a man who claims to be from Cleveland (but is actually Kane in disguise) prompts speculation that the world outside Detroit is really fine and Kane is just lying to everyone to keep his little Banana Republic under control. We never learn the truth.

Real Life

• Many timelines of the distant future either culminating in the ultimate fates of the Earth and the Solar System (which will eventually be destroyed by the Sun's aging into a red giant and subsequent death throes) and/or the ultimate fate of the universe (which will most likely be due to the universe's continued expansion gradually accelerating over time until it finally gets reduced to a cold, dark, empty void) will often tend to deliberately leave out the more imminent ultimate fate of humans altogether.

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