The humans in WALL•E depend on their ship for all sustenance. The fact that Earth has actually returned to a moderately habitable state does not change the fact that everyone, including the ship itself, believes the humans cannot live anywhere except on board the Axiom. A new credit sequence was added when the makers found out test screenings agreed with this.
In Atlantis: The Lost Empire, the Atlanteans and their city are dependent on the Crystal, which is alive and made up of the spirits of the dead royalty... or maybe all dead Atlanteans. It gives them vitality and a ridiculously long lifespan through the crystal shards around their necks which stop glowing when the power source is taken away, and Milo explicitly tells Rourke that they'll die if he doesn't return it. However, no one but the King seemed to know about the Crystal's influence, though whether they all forgot with time or never knew to begin with wasn't revealed.
Films — Live-Action
The glowy Eywa tree in Avatar stores memories and coordinates the global ecosystem, it was almost destroyed until the self defense function was triggered.
Similarly, the Unobtainium was vital to the humans. While not strictly crucial for survival, it was important for interstellar travel to mitigate the overcrowded, overindustrialized homeworld. The only use for Unobtainium shown in the film was to get to Pandora... to get more Unobtainium. No talk of colonization.
Some of the side texts do mention other uses, mostly clean mass transit. There's other mentions to various plants and animals being studied for use on earth.
In several of Isaac Asimov's stories, future humanity is fully controlled by Multivac/AC; however, "The Life and Times of Multivac" is the only one in which the dependent society becomes obliged to do without.
In another story of his, there's a subversion: An overwhelmingly large percentage of the population are incapable of doing simple math problems. When someone rediscovers how to do it by hand, a country uses it to get rid of computers in planes to make faster, lighter aircraft because they can perform the math by hand, giving them an edge on whatever country they're warring against. Note, however, that this rediscovery of basic mathematics is treated as a bad thing. The computerized status of war has meant that virtually nobody dies despite perpetual automated missile barrages going back and forth because of equally automated counter-missiles. With the rediscovery of math, the immediate reaction by the government and military officials is the potential applications of manned missiles because of how valueless human life is next to expensive computers alongside the potential logistical advantages.
A recurrent Philip K. Dick theme: after a catastrophic nuclear war or some other problem, humans are left with alien or ancient technology and have no idea how to repair or reproduce it or make any kind of technological progress.
Arthur C. Clarke's The City and the Stars. The Central Computer of Diaspar not only runs the city but actually creates its citizens' bodies using their stored memories. In a variation on this trope, the computer wants humans not to be dependent on it anymore, and has been part of a millennia long gambit by one of its creators to create a human capable of wanting freedom.
The Machine in the John W. Campbell short story of the same name. It controlled the entire Earth, and as a result the human race had become dependent on it.
Mike the computer from Robert A. Heinlein's The Moon Is a Harsh Mistress is a benign example: he helps the heroes plan a revolution, using his surveillance system and his complete control over transport, visual media and government documents. But he really doesn't care to control people's lives; he mostly wants to talk to his friends and learn the nature of humor.
Lampshaded by the main character, a computer technician, who notes that hooking everything (including the entire life support system) up to one source makes a society really vulnerable. But it was cheaper than doing it right, i.e. redundant backup computers plus manual controls for each individual colony area, and the Lunar Authority is all about doing things cheaply. It's so vital that one point in the book, a woman suggests bombing the central computer to create confusion in which they could start a revolution; the main character physically pushes her back down as she gets up - which in the female-dominated culture of Luna, is potentially a lynching offense, without a trial - so he can explain to her how terrible an idea that is. And then he tells her that he would outright murder her before he let her destroy Mike, if for no other reason than that destroying Mike would almost certainly kill the entire population of Luna: three million people.
The first MAD comic featured a story called "Blobs!" by Wally Wood which parodied this concept. You can see it here.
In Crowned Kreg series by Olga Larionova people of one planet after a catastrophe were blind from infancy and lived in symbiosis with other sentients who gave their vision via limited telepathy (and were rewarded quite well). When it turned out it's not that simple and utopian and not even close, the disagreement proved disastrous — everyone's still blind without 'em.
The cities of the Khaiem from The Long Price Quartet are dependent on the Andat for defence and economic prosperity. The andat are abstract concepts made physical that grant total power over that concept e.g. Stone-Made-Soft, Clarity-Of-Vision, Water-Moving-Down etc. The Khaiem have no military power and relatively little technology. The over-dependence on the andat is a major theme of the series.
The entire world of Matrin in The Secret Texts originally ran on enormous magic usage. Things get extremely ugly and deadly when their source gets cut off.
The universe of the Council Wars series starts out as a near Utopia: Mother controls the planet, there are a few AIs separate from her from long ago wars that fought on the winning side. Everything you could want is available. Everyone has a power allotment from Mother, although one can trade power as currency for various tasks either the AIs are unable to do or people prefer not to do (such as certain forms of medicine humans are better at). Most people just play various games or try changes to explore other forms of life. Some people choose to become Merpeople, others to fly. Some people upload to nanites. Something between World of Warcraft and LARP occupies many folks times. Various historians and folks with interest keep up random hobbies from horticulture to smithing. Some folks even change into dwarves and have fun mining. Then a political argument breaks out because humanity hasn't had any real advances in 500 years and birth rates are so low as to threaten the species. One side, believing humanity has become a Terminally Dependent Society, decides to overthrow the Status Quo. The 13 Council members then take all the power upholding the system and fight with it.
Dune's interstellar society is utterly dependent on "spice" that can only be harvested on planet Arrakis. One book even points out what would happen without the spice: hundreds of billions would die of withdrawal, interstellar navigation would be impossible, millennia-old human breeding programs would collapse, etc. When the God Emperor wants to fragment humanity forever, all he does is cause a massive spice shortage. "The spice must flow," after all.
In the short story The Ones Who Walk Away from Omelas by Ursula K. Le Guin, the prosperity of the titular city is dependent on treating some poor kid like crap. If the child's suffering was ever alleviated, all of Omelas would suffer instead. Every citizen of Omelas is made aware of this terrible price. Most of them rationalize it away as something necessary for the greater good and live their lives to the fullest knowing the cost. And then there are those who decide it isn't worth it, and walk away from Omelas.
Scott Westerfeld's Uglies takes place in a future where our current society has been destroyed due to a plague that burns up all our oil. The future society thus tries to avoid this trope, making sure to carefully manage their use of natural resources, only to be overthrown in the end since, as David lampshades, they were dependent on a mandatory operation that made everyone beautiful and stopped people from thinking for themselves and wanting things. People who wanted to think for themselves did not like this and found a way to reverse that part of the operation.
Discworld: Food might seem like a slightly obvious one to mention, but Ankh-Morpork is apparently only a few meals from going hungry even at the best of times. This problem is mostly mitigated in Raising Steam, where the advent of the steam engine makes it possible for the first time to get fresh food in the city, while simultaneously causing a population boom in the environs. Another example would be Vetinari's great Undertaking, a plan to upgrade the city's infrastructure to run off the perpetual-motion Device that the Watch confiscated from the dark dwarfs in Thud!!. The largest dwarf cities already run this way.
The final pages of The Return Of The King reveal that Elrond wore one of the three elven Rings of Power, and Galadriel is revealed to have another in The Fellowship Of The Ring. It's strongly implied that these Rings were the only real protection for Rivendell and Lothlórien, meaning that whether Sauron reclaims the One Ring and tries to dominate their bearers, or whether the One is destroyed and all other Rings left weakened, then these havens would be left vulnerable: they'd have to be abandoned, even if the elves weren't already leaving Middle-Earth.
The Lindauzi of Warren Rochelle's The Wild Boy. They were regressing to a wild state without the Iani to bond with.
In the Star Trek: Voyager novel The Nanotech War, everything on the planet Chi is dependent on nanites, to the extent that the Chiar think it pointless to try and use simple tools like hammers, because they no longer know how. Even their libraries are run entirely on nanotech; when the nanites are down, they don't even have instructions for using "primitive" tools, and seem convinced that without instructions they couldn't possibly work it out. On top of that, Chi is equally dependent on slavery; Chiar express confusion as to how the Federation economy can function without a slave caste.
In Animorphs, the Yeerks (basically plant-aliens) have to soak up Kandrona rays and liquid nutrients at least once every three days. Otherwise, they starve, slowly and painfully. This isn't a problem on their homeworld, since Kandrona is just a rare wavelength of light from their unusual star and the planet's soaking in the required nutrient pools. It's a terminal dependency on any other planet, where they rely on Yeerk pools and a technological replacement, which can be sabotaged by terrori -- uh, The Resistance.
In the Dragaera novels, the loss of the Orb in Adron's Disaster caused the Dragaeran Empire to collapse into anarchy, its government shattered and its populace ravaged by plague, invasion, and catastrophe. Only the return of Zerika from the Paths of the Dead, bearing the re-created Orb, re-started the Cycle and restored sorcery and order to the Empire.
In the Lost Fleet books, the eponymous fleet is trapped deep in enemy territory and is utterly dependent on its factory ships. These ships provide the fleet with the fuel cells and ammunition that it needs to travel and fight but they are slow and highly vulnerable to enemy attack. A major factor in any battles the fleet fights is to make sure that the factory ships are always protected.
The Colonials are reduced to 50,000 survivors after the events of the miniseries. The society that forms with the surviving humans living aboard the handful of FTL capable ships that survived the genocide fall into this trope in three ways:
1) Without the FTL technology, they would have been wiped out by the Cylons in short order.
2) The technology for spaceflight; since the 12 Colonies are now radioactive wastelands and the only habitable worlds they find also get found by the Cylons shortly thereafter, without their ships the Colonials would not survive.
3) Galactica itself; from the water filtration system that according to Commander Adama doesn't waste so much as a drop of water while cleaning a ship's supply, to the ship's DRADIS that allows early warning of Cylon attacks or its squadrons of Vipers and its powerful weapon systems, or the simple fact that none of the surviving civilian leaders are smart enough to keep the fleet together without Adama. This is proven early in Season 2 when the fleet is divided and the leaders of the civilian fleet are prone to suicidal plans.
Doctor Who: In the story "Meglos", the people of Tigella live in a city where everything is powered by a single alien artifact, which gets destroyed at the story's climax; although they're initially horrified by having to manage without it, it's presented as ultimately being an opportunity rather than a disaster.
The 2007 TV series featured Mongo as a Hydraulic Empire controlled by Ming, who had The Source, the only supply of drinkable water on the entire planet (except for the polar caps, which he controlled through a usurper in the polar regional government).
And that Source appears to be slowly running out. Which is why he's trying to develop interdimensional travel to steal Earth's water.
Revolution: Societies worldwide relied on electricity for just about everything. Of course, as soon as a worldwide blackout occurs in the pilot episode and the power stays down for fifteen years, you can be sure that society as we know it just fell apart!
Stargate SG-1: In the episode "Revisions", the computer was sending people to their deaths one by one as the power available fell below the levels required to support the population. It also altered their memories to make sure no one knew what was going on. Also interesting because the computer tricked the population into thinking they couldn't live without being constantly connected to it through an internet-like link, making everyone think they were even more dependent on it than they really were.
The Goa'uld are completely dependent on their queens to reproduce, while their Jaffa have to incubate larval symbiotes because they replace their immune systems.
Star Trek has a fondness for this trope in its various series:
Star Trek: The Next Generation episode "11001001." The Bynar home planet is run by a computer which is going to be hit by an EM pulse from a nearby supernova and get erased, so the Bynars steal Enterprise to temporarily house their computer's memory.
In the episode "Symbiosis," Enterprise encounters a ship from a planet that is suffering a species-wide plague that can only be staved off with a drug supplied by a neighboring race. It is later revealed that the plague is long gone and the symptoms the people experience are a result of withdrawal; the drug is also highly addictive. Due to the Prime Directive, Picard agrees not to reveal the truth to the suffering race, but he also refuses to help them fix their few remaining ships (they have degraded technologically) under the same pretext, so that they will eventually be unable to trade with the other race and learn the truth after massive withdrawal symptoms.
In Star Trek: Voyager, the Ocampa relied on the Caretaker and his relay to power their underground society, as well as keep them safe from the Kazon. The Caretaker himself set this up after accidental destroying the surface of their planet and shattering their culture.
In another Voyager episode, a people created a stasis system that would keep their bodies in stasis and their minds active long enough for their world to become habitable again. As time passed, their fears became manifest in the reality as a clown that would bring out a guillotine when it was unhappy. Two of the people are dead before the crew finds them another one is killed in the process of saving them from it.
The Computer in Paranoia, which was in part inspired by Logan's Run. In one adventure, when The Computer is destroyed Alpha Complex gets very dark, the air stops circulating, etc.
In Forgotten Realms, Drow culture is dependent on magical radiations so that cities were born and died when such deposits appeared and disappeared. Averted with vengeance in Sshamath, which managed to cross the deficiency period and emerge even stronger, having usual cheap solutions replaced with true arcane magic. This made it dependent on wizardry.
Most cities of Netheril were placed on artificial levitating islands. And when all magic was disabled for a minute or two... Since then, the relevant deity turns magic off "for maintenance" every few centuries, so no long-lasting civilization dares to depend on it that much.
Humanity's FTL Travel in Warhammer 40,000 is dependent upon a psychic navigational beacon called the Astronomican, without which spaceships would be lost in the Warp. This device consumes hundreds of psykers each day and is directed by the psychic might of the comatose God-Emperor of Mankind, whose life support equipment is both decaying beyond repair and happens to sit upon upon a Webway gate that could lead the Legions of Hell onto the Imperium's capitol. Not only has the Astronomican flickered and dimmed over its history, but it's also attracting the Tyranids to our galaxy.
In a less physical sense, even people in-universe have noticed that the Imperium of Man is dependent on war. Most of its interactions with its member planets revolve around tithes of materiel and manpower for its conflicts, and the draconian measures the Imperium uses to stay in power can only be justified by the number of threats surrounding it. If peace ever broke out, nobody sane would want to live under such a regime - and even in the current state of affairs, world after world chooses to rebel and try to survive on their own rather than endure further Imperial oppression.
The plasmids from BioShock fit this bill. Everyone used them and they turn out to naturally hover between being Super and Psycho Serum (depending on which you took and if you abused them). Then a civil war breaks out and Ryan had them laced with mind control agents. So, needless to say, this terminally dependent society OD'd.
The Iifa Tree and the Mist from Final Fantasy IX are a mild example, because the heroes find an alternative energy source.
The city of Lea Monde from Vagrant Story was designed as a city-sized spell. The game takes place long after the city has already collapsed on itself.
Interstellar travel in Mass Effect is impractical without the mass relays, all of which are under the control of the Reapers. If the various races took the time to develop their own means of faster than light travel, it would solve a lot of problems. This comes up in Mass Effect 2 - the asari bartender on Illium complains that she became a laughingstock for suggesting they try to build their own mass relays. The protheans' prototype may not have saved them, but in Mass Effect 3 it may be enough to save galactic civilization 50,000 years later.
This is the reason for the Inferred Holocaust of Mass Effect 3's original ending - regardless of what choice you made, the mass relays are destroyed, leaving a massive fleet of aliens with a variety of dietary needs stranded over a ruined Earth, and presumably leading to the collapse of interstellar civilization.
The quarians live on a flotilla of ships in space, and are dependent on their giant greenhouse ships for all their food supplies. So much so that these are kept at the heart of the flotilla for their protection.
High Elves and Blood Elves in World of Warcraft are dependent on magical energy, without which they become physically and mentally twisted husks called "Wretched". Night Elves suffer a similar affliction, but their need for magic is supplied by moonwells.
Goblins are somewhat dependent on kaja'mite for their superior intelligence. As the supplies have dwindled and they resort to more diluted forms, goblin society and technology has declined.
In Phantasy Star II, the terraforming on Mota and the carefree lifestyle of its people are dependent on Mother Brain for everything. Three guesses on what happens to her and what happens to Motavia in between II and IV.
In Armored Core For Answer, much of humanity (those who could afford it, at least) is dependent on the Cradle habitats they live in. One option the player can take later is to side with Old King and bring them down for the lulz. Maximillian Thermidor also wants to take them down, but this is because he believes that they are a temporary solution at best and that destroying them would open up the way for humanity to get to space.
In Star Control 2, the Utwig are highly dependent on the Ultron, a precursor artifact which gives them prophetic powers. When it breaks, the Utwig enter a perpetual state of mourning and are too depressed to do anything. Hilariously, everyone else is convinced that the artifact is absolutely useless. Whether it actually does anything is left ambiguous.
It is made clear that the Utwig are highly dependent on the Ultron simply because its breaking made them enter a perpetual state of mourning (since they were convinced of its power). This has nothing to do with whether the Ultron actually does anything, it's just that they didn't get the Ultron until shortly before breaking it, and that breaking happened at most a few years back.
The human population of Cocoon in Final Fantasy XIII depend on the Fal'Cie for everything. There are a few million Fal'Cie in Cocoon and each one handles a different function to keep the artificial world running. Among the Cocoon Fal'Cie we see in the game, there's a Fal'Cie in charge of running power plants, one that handles food production, another one acts as Cocoon's artificial sun, the Fal'Cie Eden is the Internet, Barthandelus acts as the overseer of them all and has the most freedom to act, and there's Orphan who provides the power that keeps the other Cocoon Fal'Cie alive. Without the Fal'Cie especially Orphan Cocoon would fall apart. The Pulse Fal'Cie on the other hand seem more geared towards terraforming Gran Pulse.
The world in Magna Carta II has unnaturally high levels of ambient magic, thanks to the Hero of Legend. It is specifically noted that with so much magic around, nobody has had to farm for food for at least a thousand years. The heros end up having to bring the levels back to normal and force society to labor for sustenance for the first time in generations, as it turns out that the high magic levels are maintained via world wars and human sacrifice of a specific soldier every 250 years or so.
Fallout 1 starts with the main character being sent out of the Vault to find a new water chip, without which the Vault will run out of clean water. In fairness, the people behind the Vault project realized how dependent their populations would be on the Vaults' equipment, it's just that in Vault 13's case a shipping error left them with no spare water chips.
Of course, things were worse in the Vaults that were secretly designed as social experiments. One we set up so its equipment would regularly fail, as a stress-test for possible space travel. Even more so for Vault 112, where the residents have been imprisoned in a Lotus-Eater Machine simulation for 200 years and are incapable of survival outside of it.
In Myst III: Exile, Saavedro's civilization was completely dependent on the Lattice Tree's good health for survival.
In the Aligned continuity, Cybertronians are dependent on Energon. Granted, there is essentially oceans of the stuff, right up until Megatron corrupted the Core of Cybertron and it eventually had to be shut down. Transformers: Fall of Cybertron deals with the aftermath of this. There is a synthetic version, but the formula for it was sent off into space to prevent Megatron from getting hold of it.
In Tales of the Abyss, the entire world is dependent on The Score, which is part ancient prophecy and partly a history of the entire planet, from start to finish, with every single detail of existence available for the asking by those who are capable of reading it. Since the Score Yulia read for the planet long ago predicted a prosperous future, devoutness in the local religion means relying on the Score for every decision, no matter how minor, because obedience to the Score will bring the predicted future to pass. Eventually, it's revealed to have gone off-track, and that the formerly-lost end of Yulia's Score predicts the destruction of the world as a direct result of events that happen during the game, and as a result people have to learn to live without it and make their own decisions. NPC reactions vary from wanting it back to enjoying their newfound freedom.
Galactic Civilizations II: Twilight of the Arnor: the Yor tech tree reveals that they are dependent on something on Iconia, known only as the Spark of Life, to be AI rather than robots, with the effect wearing off in time. The reproductive rate enhancement tech involves studying the Spark's energy to extend its effects, and the planetside structures that spring from this involve channelling Spark energy to other worlds. How this works with planetary conquest is not known; presumably the Yor pick up the Spark of Life, load it onto the fastest ship they have, and run like the clappers.
Orion's Arm has a serious problem with people developing Baseline Hyperdependency Syndrome (that is: humans are spoiled rotten by the AIs) and nothing has even gone wrong yet, although many groups predict that collapse is imminent.
Neopets' Darigan Citadel was once a normal medieval town, until someone stole the magic orb fertilizing their crops. Now the land is about as fertile as a cinder block.
Mother in Dresden Codak: a world-assimilating AI/ Grey Goo /Singularity that provides everything Humanity asks for - to point of making people unnecessary, irrelevant and progressively infantile. They go to the verge of extinction as life in the virtual worlds she/it provides takes precedence over breeding. When humanity finally goes to war with Mother, victory comes at a terrible cost: much of human history and culture dies with Mother, and every human is blinded.
There are a little over seven billion people on this planet; before the nineteenth century it was a few hundred million, reaching the one billion mark around 1800 and still less than two billion in 1900, and more doubled in the last 50 years. Without our advanced technology, most of us would die. Horribly.
It's worth noting, however, that this advanced technology we rely on so heavily is designed and created by our own hands, and we use that technology to better prepare for and avert disasters in which we might lose access to working advanced technology. Indeed, many people are quite capable of not only surviving without technology using basic survival skills, they're capable of slowly recreating the technology that improves their lives and well-being, starting society back up again.
Electricity. It is our Applied Phlebotinum, used for everything from navigation, communication and information storage to food storage and preparation. And then one tree falls...
...and someone comes along to repair it, relatively promptly. It's also not exactly Applied Phlebotinum, since we have a thorough understanding of how it works, how to generate more of it, and where it comes from. The problem, rather, is that our society uses technology and electricity to attain a vastly higher level of population, functioning, and productivity than would otherwise be possible—when an overwhelming disaster strikes and cripples that infrastructure past the breaking point, the society is no longer sustainable for obvious reasons. Still...worst case, you'd end up with a society that crashes down to the level that it would otherwise have been stuck at from the beginning.
All the monocultured staple crops such as corn and wheat. If disease or climate change devastates them....
Every society or species, real, imaginary, sentient or otherwise is terminally dependent on something, oftentimes something which is completely taken for granted. For example, all life on earth is highly dependent on a massive hydrogen guzzling fusion engine in the sky, which we call the sun. The difference between continued existence and annihilation usually hinges on how tamper proof and/or sustainable that something is. In this case, our massive, flaming fusion plant is fairly tamper-resistant and looks to last quite some time.
As seen in Crippling Overspecialization, many animal species are terminally dependent on a specific food or environment, such as giant pandas (bamboo) and polar bears (the vanishing sea ice).
A government that takes advantage of this, specifically water needed to irrigate fields, is known as a hydraulic state. Note that there's a lot of debate over whether or not dependence on irrigation leads to despotism — it doesn't help that Wittfogel's term for this was "Oriental Despotism"...
Raise your hands, tropers: how long could you stay sane if the internet up and disappeared?
Earthlike planets cannot support life without liquid water on its surface. If its parent star starts to leave the main-sequence stage, said planet's temperature will exceed that of the boiling point of water, and the results will be self-explanatory. Also, plate tectonics cannot exist without liquid oceans. Guess what happens in about 1 billion years!
This can happen to countries who rely on cash crop farming to support their economies, especially in developing countries such as areas of Africa in the form of cotton and rubber to provide for its citizens and cover its expenses.
The plight of bees worldwide has led many to speculate on how hard it would be for us to pollinate all the plants we rely on without them.
Can also apply to the bees themselves, especially those bred to harvest pollen from only a specific number of flowers.
The Haredi Jews in Israel consistently grow in number, and their children are pushed towards religious scholar success more than economic success - hence they're usually taught religious subjects almost exclusively, and their leaders are often vehemently opposed to getting them taught subjects such as English and mathematics. Thus they usually live in constant crippling poverty, relying mostly on the non-Haredi society’s taxpayer money for their meager pensions (each Haredi Jew gets just enough to live and support his family, but as they consistently grow in number this has a massive negative impact on Israeli society, as OECD reports show). Israeli Minister of Internal Affairs Eli Yishai (who is a Haredi Jew himself) once uttered a notoriously stupid statement saying that a completely Haredi city is preposterous, as it would never be able to support itself. Fortunately, this situation is changing, as the State of Israel seems to be making efforts to incorporate them into the work force and into military service, by trying to work out a ‘super-kosher’ solution for them.note They often avoid work and service not just to focus on their studies, but also because the conditions they have to work/serve in, such as working/serving alongside or maybe even under women, would go against the strictness of their religious rules; in case you were wondering, this is a problem mostly in Israel and not elsewhere because according to Jewish law, Jews have to be extra strict in the Land of Israel. You are more than welcome to keep your opinions about how effective or earnest this is, or what the implications for women or non-Jews would be, to yourself.
Any exclusively dedicated religious group or organization really has the same problem. They rely on others to support them, so something as simple as an opposing idea gaining prominence can cause an entire religious hierarchy to collapse or reform into a new version.
Most, if not all dictatorships justify their power by claiming that the country is a society of this type. Of course, if that is actually true or just an excuse of the dictator depends on each specific case, and may be open to discussion. And better leave it at that, and avoid specific names.
Oil. Powers every major form of freight transport, and it takes several million years to form. It'll run out eventually, and considering how many After the End or Bad Future scenarios are caused by the oil running out, we might go this way if we don't find alternative fuel sources.
Fossil fuels, in general. There's not much you can do with oil that you can't do with natural gas and coal, even if you can't always do it as cheaply or efficiently, but, like oil, natural gas and coal formed over millions of years and they, too, can be used up.
Hopefully that may change with the introduction of alternatives to fossil fuels such as solar energy and biomass fuel, but full integration into those new sources would still be difficult.
This is arguably the state of any civilization advanced enough for people to specialize, so that some are able to produce a surplus of food while others are able to spend their time on TV Tropes rather than farming. From feudal aristocrats to Nobel scholars, a lot of people would starve to death if they couldn't get their food from a marketplace.