No Blood for Phlebotinum

""War never changes. In the 21st century wars were still fought over the resources that could be acquired...""

- Fallout

""When goods do not cross borders, soldiers will.""

- Frederic Bastiat

Nearly every conflict in human history has been over a resource of some kind. Land, water, food, oil, mineral rights, timber, livestock, labor... something other than national pride or honor and glory is usually lurking around as subtext whenever man kills man on the field of battle.

The local Unobtanium, Green Rocks, Spice of Life, Minovsky Particles, Vespene Gas or Imported Alien Phlebotinum are all naturally rare and valuable, so much that everybody wants to get their hands on it. Quite naturally, this can lead to world- or galaxy-wide wars over the damn stuff. Caught up in the middle are the usual tragic bystanders, for whom your magical miracle substances are Worthless Yellow Rocks. Things will get... interesting if the resource in question turns out to be Aesoptinium that decides it doesn't want people fighting over it and sets up a No MacGuffin, No Winner scenario.

Anime and Manga

 * Transformers Energon was all about fighting over and using the titular Green Rocks.
 * Transformers is usually about that in general, be it energon, Planet Keys, or Allspark fragments. Transformers Armada had Mini-Cons, which were sentient phlebotinum.
 * Beast Wars had this in the first season, where the Maximals and Predacons fought over a planet rich in raw energon. Of course, by season 2 they found plenty of other things to keep fighting over.
 * In Code Geass, Japan was attacked by Britannia essentially because it was sitting on the largest Sakuradite reserves on the planet.
 * Or, possibly, the even more critical phlebotinum,.
 * E2 energy from Another Century's Episode and A.C.E 2
 * Darker than Black had Heaven's War, a Melee a Trois in the backstory where pretty much everyone was trying to get control of Heaven's Gate in Brazil. It only ended when most of South America got replaced with big "unaccessible" circle on the map.
 * Shortly before the events of the main series, the world of Mobile Suit Gundam 00 was subject to the "solar power wars". When advanced solar technologies were discovered, oil suddenly became relatively worthless, leading to a number of Middle Eastern countries continually splitting apart into new ones. To harness the technology, countries needed to build space elevators, and this lead to blocs of nations forming who jealously guarded their elevators and were constantly at the brink of war with the other blocs.

Film

 * The whole point of James Cameron's Avatar. It's even called Unobtanium.
 * All Phlebotinum in District 9 has a biological component, so while everybody is stockpiling BFGs, only the slum residents can use them.

Literature

 * Dune had its Spice, a resource so vital that whoever owns Arrakis, the only planet that produce them, will have a huge power over other planets. Several novels have story arcs where someone attempts (unsuccessfully) to break the Arrakis monopoly on spice by transplanting a Sand Worm to another planet, creating a spice substitute, etc.
 * The Lord of the Rings: The Ring, obviously.
 * Except the Ring is not what the war is about. It is about whether or not people of Middle Earth will be ruled by Sauron. The ring is just one of the weapons.
 * Also Mithril in the supplemental material, and the eponymous silmarils in The Silmarillion. And the dwarven treasure horde taken by Smaug in The Hobbit.
 * Pynvium in Janice Hardy's The Shifter can absorb pain. Its mines are important enough to fight over, but it's when that the plot kicks in.

Live-Action TV

 * In the Star Trek universe, the Klingons and Federation sometimes fought over sources of dilithium crystals (e.g. the Star Trek: The Original Series episode "Elaan of Troyius"). In Star Trek IV: The Voyage Home, Scotty and Spock invent a way to "recycle" it with particles stolen from "nuclear wessels", thus making it less rare by the Next Generation era.
 * In an episode of Star Trek: Enterprise, a planet was raided for deuterium. The writers Did Not Do the Research... although given the existence of things like the Oklo natural nuclear reactors in Gabon, who's to say that there isn't some way the planet could have produced and/or received abnormally large amounts of heavy hydrogen?
 * In the first Star Trek Shatnerverse novel, Chekov and Uhura are engaged in an undercover operation and pretend to deal with a shady Klingon. He offers dilithium as payment. Chekov brushes him off, saying it's nearly worthless now, ever since the whole "nuclear wessels" discovery (i.e. ships can run forever on a single set of dilithium crystals without needing to replace them).
 * Somewhat bizarrely, in Star Trek: Voyager, the Kazon, an oxygen-breathing species traveling in hydrogen-powered ships, will kill, steal, or trade hostages for water. When he first arrives on the ship, Neelix seems similarly surprised by Alpha quadrant water technology.
 * That's mainly because the Kazon are Too Dumb to Live. The Borg refuse to assimilate them because of that.
 * A classic Doctor Who had one of these, in the episode "The Caves of Androzani". It was over spectrox, "the most valuable substance in the universe."

Music
"The scavengers soon will rule Waging war for a tank of fuel"
 * "Roadkill (...or Be Killed)" by Steelwing:

Tabletop Games

 * Warhammer 40,000
 * Promethium (a catch-all term for oil-like flammable substances) is critical to the war machines of at least three factions - the Orks, the Imperium, and Chaos. Expect frequent conflicts over promethium mines and refineries, since the Imperium is the only group that bothers to build them instead of just stealing the stuff from everyone else.
 * The same goes for many natural resources, from less common ores to Nephium (a toxic exotic substance with variety of uses, mined on some planetoids) - in Rogue Trader had two strongest dynasties come to blows over a rich source of the latter until they had to settle on division.
 * The "Archeotech" (among the Human factions) and various more ancient artifacts (in general).
 * Dungeons & Dragons in various settings have a lot of wars in various settings over a local source of something valuable or trade route allowing access to it.
 * Dark Sun over... well, just about anything that can help to survive or give one an edge, from water sources to obsidian mines.
 * Forgotten Realms has Zhentarim trying to control trade over the whole continent, thus their fortified bases (like Darkhold) tend to sit in a spitting distance of some or other trade route.
 * Spelljammer has kindori fat used for e.g. lamps, and most Greek Fire made from it. As a result, kindori riders occasionally clash with space whalers; they collect and sell fat only when kindori die of natural causes, of course - the creatures that can carry a village don't reproduce like rabbits and are just too valuable.

Toys

 * The whole Bionicle story has its roots in the Core War, a massive world war over Energized Protodermis that emerged from the core of the planet, the unstable nature of which ended up splitting Spherus Magna into three.

Video Games

 * The Command & Conquer Tiberium series revolves around an alien crystal that's extremely rich in resources, leading to several Tiberium Wars fueled by or fought over the stuff. Of course, it's the fight against tiberium that's the real danger...
 * Humans fought a really big war over Imulsion in the Backstory to Gears of War, before the scary underground alien invasion.
 * "Ragnite" was one of the reasons behind the war in Valkyria Chronicles, with the player's small neutral country caught right in the middle due to its large natural deposits of it.
 * Tarydium in the Unreal series.
 * "Nectar" in Haze. Not in any way a stand-in for a certain other resource found in South America.
 * Practically inevitable in the later installments of Civilization if you want your faction to prosper, unless you get really lucky with city placement or allies. If you do not have era-appropriate strategic resources, expect to be invaded by other civilizations who do and consider you easy pickings. If you have era-appropriate strategic resources, expect to be invaded by other civilizations who do not have it and desperately want it. Either way, wars are almost certainly going to be fought over it.
 * Final Fantasy VII features the miracle substance Mako. Generated from the essences of creatures long-since dead and pumped from the ground, it has allowed the company controlling it to control world politics, and its overuse creates serious consequences for the planet... similar to a certain black substance that the people of Earth have been using for several decades with similar results. This certain black substance is later treated as a viable alternative to mako in Advent Children.
 * There's a bit in Shinra's headquarters where they have a set of advertisements for the line of cars that they make (represented during the opening FMV). The video clearly shows the engines of said cars using Mako in a way that is analogous to the use of the... distillates of the aforementioned black substance. (And "The Aforementioned Black Substance" would make a great band name.)
 * The Fallout series' backstory mentions conflicts over the world's dwindling oil reserves between the 2050's and 70's. The European Coalition invaded the Middle East once oil prices rose too high, though these Resource Wars ended suddenly once the last of the petroleum in the region was tapped out. With Alaska containing the last oil on the whole planet, China invaded America in a conflict that led to a global nuclear war, hence the game's post-apocalyptic setting.