History ApocalypseHow / Class1

* In ''Literature/TheDreamsideRoad'', governments the world over shut down during a [[GreatOffscreenWar global terrorist attack]], five years before the story begins. Most never returned.

* In the ''TabletopGame/{{Cyberpunk}}'' setting has a notable one in the form of the DATAKRASH virus, It's revealed the netrunner Rache Bartmoss set up a dead man's switch that would activate two weeks after he died, which ended up happening in 2023 of their timeline. The virus itself first started small doing things that'd be consider minor glitches like swapping small piece of code here and there, by the time it was identified as a virus by others it had become more damaging to the point the only thing to do was quarantine sections of the internet from usage. In the end nearly 80% of the internet was rendered unusable before it was officially quarantined completely. Due to the scale of the damage and safety concerns of potential reinfection, the world of cyberpunk as of '' 2039'' has mostly restored to short range LAN connections. As of the events of '' Cyberpunk2077'', long ranges connections have become available for the rich but nothing on the scale of old internet.

* The Second Impact in the backstory of ''Anime/NeonGenesisEvangelion'', which killed over half of human population, rose the sea level enough to submerge entire cities and heavily altered the climate. By the time the series proper begins, civilization has gotten back on its feet in some places, but the almost complete emptiness of Toyko-3, the city the series is set in, is heavily emphasized during the series.

* ''Anime/HeatGuyJ'' As explained in a BreakingSpeech given by [[DesignatedVillain Clair]], the people of Earth got a hold of the AppliedPhlebotinum of the resident SuperiorSpecies. That was fine, until they started using said phlebotinum [[NuclearWeaponsTaboo for war]], and most of the population of Earth was wiped out, save for a few hundred-thousand people, who now live in seven isolated city-states (and some small towns/villages surrounding them.)

* In ''Fanfic/TokimekiPokeLiveAndTwinbee'', [[spoiler:[[OriginalCharacter Aleena]] reveals in "Prophecy of Failure!?" that outside of northern places in Canada, Siberia and Greenland and presumably southerly places like New Zealand and West Antarctica, civilization has collapsed due to ClimateChange and wars for limited resources are the norm]].

* The effects of climate change can easily do this, even if humans get time to adapt to the changing world. The most immediate effects start with a rise in water levels due to the melting ice caps, which means very little to us now, but in the future this rise could sink coastal cities that are unprepared to handle them. Worse, this shift in the ocean would result in the alteration of ocean currents which would radically change the weather. For example, hurricanes have been happening more frequently in America and increasingly more powerful. Some areas, like the American Southwest, are experiencing a major decrease in rainfall, rendering those areas unlivable for humans due to the lack of easily accessible water, and forest fires more severe and frequent. The climate, on average, will get hotter around the globe, but climate and weather are very different things, meaning winters could be colder (as with the collapse of the Polar Vortex which devastated North America in the winter of 2013) and snowier. A change in climate, even one as small as a few degrees Fahrenheit, could cause widespread crop failure and famine. Food prices would go up, economies would collapse, and waves of refugees would flee from equatorial areas to more habitable regions, putting further strain on the available food supply. The increased natural disasters could also result in a collapse of infrastructure, including hospitals, roads, and emergency services, causing thousands to die. It isn't all bad though; at least the northerners get to have sunnier weather on average. It just comes at the cost of immense human suffering and lives, of course.

* There are a number of Supervolcanoes on Earth and we get approximately one big eruption every 100,000 years. One example is the Yellowstone supervolcano, which could cause a Class 1 event for America thanks to the spread of lava and ash, and possibly even cause another Ice Age if the ash stays in the atmosphere long enough. [[FridgeHorror While the Yellowstone supervolcano]] [[OhCrap is overdue for an eruption]], it's showing no signs of doing so (we would know months in advance thanks to seismic activity) and may never erupt again - but don't be disappointed, it's only the 21st most dangerous volcano in America.

* In ''Fanfic/TokimekiPokeLiveAndTwinbee'', [[spoiler:[[OriginalCharacter Aleena]] reveals in "Prophecy of Failure!?" that outside of northern places in Canada, Siberia and Greenland and presumably southerly places like New Zealand and West Antarctica, civilization has collapsed due to [[GlobalWarming Climate Change]] and wars for limited resources are the norm]].

* ''Series/DoctorWho'' manages a Class 1 in the series 3 finale, [[Recap/DoctorWhoS29E12TheSoundOfDrums "The Sound of Drums"]] and [[Recap/DoctorWhoS29E13LastOfTheTimeLords "Last of the Time Lords"]]. Human life on Earth is ordered decimated the old-fashioned way — 10% of the population gets killed while the Master takes control of the planet and enslaves the remainder of humanity. Later, we hear about the ruins of New York, the fusion mills of China and the radiation pits of Europe. Thankfully this gets a ResetButton.

* ''Fanfic/KimiNoNaIowa'': The abyssals' stated goal, the genocide of Japan and the USA, combines this with '''Regional Species Extinction'''. The death of almost half a billion is, from a purely numerical perspective, definitely survivable for humanity, but the cultural, economic and scientific losses will continue to be felt for years if not decades to come, to say nothing of the security implications of America ceasing to exist as world policeman. The addition of the other nations named in the VillainSong in Chapter 31 - Russia, the UK, China, India, and Australia - if they refuse to kowtow to the abyssals and help destroy Japan would elevate the damage to the equivalent of ''Continental Species Extinction'' if not low-level ''Planetary Societal Collapse''. While the death of around 3 billion still leaves half of humanity alive, enough survivors to meet minimum viable population and avoid inbreeding and genetic drift, the loss of China alone and its leading industrial capacity would put the rest of the world in a bad place while frantically trying to compensate, never mind the destruction of the other named nations. By this point, what else the abyssals have hit, including much of Western Europe and Southeast Asia, is merely an ugly cherry on top.

* In ''Fanfic/TokimekiPokeLiveAndTwinbee'', [[spoiler:[[OriginalCharacter Aleena]] reveals in "Prophecy of Failure!?" that outside of northern places in Canada, Siberia and Greenland and presumably southerly places like New Zealand and West Antarctica, civilization has collapsed due to [[GlobalWarming Climate Change]] and wars for limited rescources are the norm]].

* In ''VisualNovel/DanganronpaTriggerHappyHavoc'', presumably an event of this scale has happened before the events of the game.

->'''Thanos:''' Going to bed hungry. Scrounging for scraps. Your planet was on the brink of collapse. I was the one who stopped that. You know what’s happened since then? The children born have known nothing but full bellies and clear skies. It’s a paradise.\\
'''Gamora:''' Because you murdered half the planet!\\
'''Thanos:''' A small price to pay for salvation.
-->-- ''Film/AvengersInfinityWar''

* There are a number of Supervolcanos on Earth and we get approximately one big eruption every 100,000 years. One example is the Yellowstone supervolcano, which could cause a Class 1 event for America thanks to the spread of lava and ash, and possibly even cause another Ice Age if the ash stays in the atmosphere long enough. [[FridgeHorror While the Yellowstone supervolcano]] [[OhCrap is overdue for an eruption]], it's showing no signs of doing so (we would know months in advance thanks to seismic activity) and may never erupt again - but don't be disappointed, it's only the 21st most dangerous volcano in America.

* ''Webcomic/{{Magellan}}'': The Q'Arth invasion of 1972 - an incursion of soul sucking, NighInvulnerable demons from another dimension that killed more than 10 million people in less than a day - all but destroyed the Soviet Union, politically[[note]]It still exists as a remnant in the strip's current continuity, but nowhere near the power it once was.[[/note]], destroyed Moscow and its' surrounding area [[NukeEm literally]] and basically altered the social nad political landscape of the Magellanverse's Earth forever.

* ''Franchise/{{Halo}}'': By the time ''VideoGame/{{Halo 3}}'' rolls around, humanity is in a position like this, with most non-Earth colonies having been utterly annihilated, its military reduced to a handful of fleets, and the war having killed 23 billion humans out of an estimated pre-war population of 39 billion. Nonetheless, the surviving human worlds are still able to maintain their high-tech civilizations, and after the Human-Covenant War ends, humanity as a whole is in ''just'' good enough shape to start reclaiming their lost worlds.

* In Creator/GregBear's ''Literature/BloodMusic'', artificially enhanced lymphocytes gain intelligence and spread quickly across the entire North American continent, converting all biomass into more entities like themselves. (Although they are capable of encoding and converting intelligences into their cellular-level versions, so nobody strictly "dies" during the epidemic.) After the incident resolves itself, North America has been wiped clean and humanity in the rest of the world is trying to adjust [[spoiler: to new laws of physics. The intelligences in North America caused the laws of physics to fracture slightly due to the density of observation causing the laws of physics unable to follow their own rules. Surprisingly this is not HandWavium, there are real scientific theories behind such an event, as unlikely as it is to ever occur. Think of a well-regarded theory such as Heinsenberg's Uncertainty Principle which implies that, for any given particle, you can know its position or velocity, but never both, as an observation of one will affect, and therefore prevent observation of the other. Now imagine that someone develops the technology to accurately observe and record both. There is some uncertainty (no pun intended) as to what might actually happen to the observed particle at this point.]]