Shattered Stability - Casus Belli.
Prussia, Denmark, France - This is a call to arms!
England stood no chance - This is a call to arms!
But we couldn't be happier, now that he attacked,
We have Casus Belli!note
The leaders of Viridia and Tyria want to go to war. Not for a silly reason, but due to anything from good old fashioned jingoism, greed, political/economic/religious differences, or a simple historical grudge. However, they can't just out and out declare war, that would be uncivilized! And more importantly, it would make them look bad to the international community, which isn't good politics. So instead they will wait for or manufacture a Pretext for War out of whatever should come their way.
Did a Tyrian pig farmer lose a pig when it wandered into Viridia? This Means War! Maybe a Viridian girl disappeared near the Tyrian border? Tyrian slavers must want to capture Viridian women since theirs are so ugly! A favorite is for Star-Crossed Lovers from both sides (preferably royalty) to elope, causing both sides to assume the other kidnapped their heir.
One interesting and ironic variant is when hardline elements from both sides will collaborate to stage a high profile assassination or other incident to kickstart a war, proving just how well they work together to achieve their goals despite hating each other's guts. This one is especially common when one or both nations have a Reasonable Authority Figure as a head of state, since it can force their hand to war, or if they're the assassination target, get them out of the picture and make them an unwitting martyr. False Flag Operation is one of the classical moves too, and almost a Twentieth Century theme song.
Point is, an incident any two sane heads of state would quietly defuse is treated as a Rant-Inducing Slight in order to start the war. In these cases, heroes typically have to uncover the plot in order to Prevent the War.
A technical term for this is the Latin term Casus Belli, or case for war.
Since wars of aggression have technically been banned, you'll find that these are a lot more common today than they were previously, since both sides are at pains to show that the other side started it. As a result, the history of many a 20th-century war reads like a really, really dark Idiot "Fawlty Towers" Plot. Mind you, "civilized" countries have more or less always deemed it improper to declare war on your neighbors "because we want your stuff" or "because we feel like it;"note even an aggressive war would have to have some kind of triggering incursion, insult, or violation behind it. (Look up how each of the three Punic Wars got started—the pretexts are hilariously flimsy.)
See also War for Fun and Profit.
- Crest of the Stars: The United Mankind attacks an Abh ship through a previously unknown hyperspace lane, then declares that they were attacked first and destroyed the ship in self-defense. They use this incident to begin stirring up their allies and begin to build an excuse to go to war with the Abh. The Abh Empress doesn't believe for an instant that the Abh ship is to blame, realizes what the United Mankind is up to, and decides to just cut to the chase and declare war immediately, which catches the United Mankind and their allies off-guard.
- The plot of Aldnoah.Zero is kicked off when Princess Asseylum Vers Allusia, the granddaughter of the emperor of Mars, is assassinated in a terrorist attack on Earth during her diplomatic mission. The Orbital Knights, the Martian warrior nobility, react immediately with a full-scale invasion of Earth. Unbeknownst to the majority of the knights, the assassination was a False Flag Attack perpetrated by a faction of their own government in order to force the conquest of Earth.
- A heroic example occurs in Yu-Gi-Oh! ARC-V, with LID (Group A) taking advantage of the team from Duel Academy (Group B) going to Paradise City (part of A's territory) on a mission to kidnap two Living MacGuffin characters. Group A gets footage of B's soldiers using hyper-advanced Magi Tech weapons to seal the souls of (metaphor for murder) bystanders that get caught in the crossfire. The propaganda created from the footage convinces the people of A's home that B is invading, and that they must militarize and fight back. The reason why it's a heroic example is because B already has invaded a different dimension and committed genocide upon it's inhabitants; it just hasn't moved onto A's home yet, and the people running A want to ensure that their home is capable of defending itself when the need arises.
- The finale of Starship Operators, the Earth Alliance invades the Henrietta Sector on the pretext of defending the Kiba government-in-exile onboard the Amaterasu from the Kingdom. However the Amaterasu crew decide they'd rather not be used like that.
- Tintin: The Broken Ear: A Corrupt Corporate Executive encourages Tintin (then working as the aide to a Banana Republic's dictator) to declare war on a neighbouring country. Tintin point-blank refuses, so the executive frames him and he's forced to flee the country in a staff car. The car is fired upon by the border guards and the incident is then used as an excuse for war.
- Before that, in Tintin: The Blue Lotus, there was a thinly disguised replay of the Mukden Incident used as a pretext for additional Japanese intervention in China.
- Fury MAX: An ex-Hydra agent named Gagarin meets up with Fury and suggests that they start a war somewhere to give each other something to do (what with the Soviet Union gone, SHIELD has suffered major budget cuts and is now led by an Obstructive Bureaucrat. Gagarin proceeds to start a war in a island Banana Republic and does everything he can to escalate the conflict, with Fury barely preventing a full world war, killing the man himself but losing his squad. And to his horror, Gagarin's last words ring true in his mind: That if Gagarin hadn't done it, Fury would have.
- What About Witch Queen?:
- The final reason for Arendelle and Weselton to go to war is scout shooting incident, which is a result of tensions building up to the point that two armies are less than a mile from each other. Schemers on both sides set the entire situation up (sending armies, choosing General Ripper to be one of the commanders) so it would end that way.
- Hans' plan to keep Westerguard is to start war between Isles and Arendelle by killing Anna and making it look as if it's Islanders' fault.
- At one point in Earth's Alien History, the Terran Treaty Organization colonizes the Rama star cluster, which the Invincible Ctarl-Ctarl Empire claims to have already put a stake in (despite never colonizing or occupying). To try and rectify this, Ctarl-Ctarl ambassador Aisha Clanclan conspires with a high-ranked friend in the military to place a fleet on a "training exercise" on the border, in the hopes that they'll be fired upon by TeTO, enabling them to start a war that will result in the Ctarl-Ctarl taking the cluster for themselves. Except the resulting border skirmish never escalates into a full-scale war, and TeTO puts more effort into it, so the Ctarl-Ctarl get their asses kicked.
- The Marx Brothers' Duck Soup. Essentially just bankruptcy and personal slights. Some of which were hypothetical slights that didn't actually happen, at that.
- The plot behind The Princess Bride.
- Star Trek VI: The Undiscovered Country featured a combined conspiracy by both Starfleet officers and Klingon military leaders to try to veer both nations onto the path to war by having each side's Reasonable Authority Figure assassinated by agents from the other side. Given how the Federation was definitely in the stronger economic and military position at the time, many fans have since hypothesized that the respective Klingons were goaded into "dying on their feet rather than living on their knees" by Section 31 machinations.
- The novel "Sarek" indicates that the the actual masterminds behind this plot were the Romulans, who in the movie had seemed to just be bit players.
- In Star Trek Into Darkness, Admiral Marcus sent Kirk and the Enterprise into Klingon space to take down John Harrison, then sabotaged the Enterprise's warp engines so they would be easy prey for the Klingons, using the destruction of the Enterprise as a pretext to start a war with the Klingon Empire.
- Star Wars has many thanks to the machinations of Chancellor Palpatine. In The Phantom Menace, he directs the Trade Federation to invade Naboo over a trivial dispute, and in Attack of the Clones he deploys the clone army secretly created by his apprentice Count Dooku to Geonosis, sparking the Clone Wars.
- A very common reading of Starship Troopers is this. The meteor strike that the Federation blames on the bugs is incredibly suspect; there's no stated evidence for it and propelling an asteroid across many light-years at apparently sublight speed makes absolutely no sense. Given the personality of the Federation, it's much more likely that the impact was either a natural disaster or even orchestrated by them, and then credited to the bugs.
- When Guy de Lusignan becomes King of Jerusalem in Kingdom of Heaven, he releases Reynald in order for him to do something to start a war with Saladin. In an earlier scene Saladin's adviser had remarked that Guy becoming king meant Saladin didn't have to find one himself since the man was stupid enough to start a war he couldn't win.
- In The Man Who Knew Too Little, members of the British and Russian intelligence services are collaborating together for a bombing that would take out the top table of a British/Russian peace conference. The British spymaster is seen longing for the new funding, equipment, and poisons that renewed tensions would bring. When the hero unwittingly starts getting in the way, the Russian spymaster complains, "If we cannot trust each other, how can we bring back Cold War together?"
- In the political satire Wrong Is Right (1982), two suitcase nukes acquired by a Middle Eastern dictator are found on top of the World Trade Center. After being successfully disarmed, they're used to justify invading that country and seizing its oil. The last thing we see of the dictator as he's being bombed is him complaining that the whole thing was a set-up, as he still has the nukes in his possession. The movie became Harsher in Hindsight after the events of 9/11.
- Aquaman has King Orm using an empty remote-controlled military submarine in a False Flag Operation to attack him and King Nereus, all to convince Nereus and their respective kingdoms that the surface world is enough of a threat to go to war with. In fact, Nereus isn't fooled for a moment, but since he also wants war with the surface, he plays along.
- Mocked in 1066 and All That, which names the countries principally involved in fighting and where the fighting took place in The Crimean War and World War I after describing the incidents that precipitating them involving entirely different countries.
- Discussed in the Tom Clancy novel The Bear and the Dragon. China is considering initiating a war of aggression against Russia, and Russian observation planes are staying well within Russian air space, but examining the Chinese preparations. The Chinese war minister recommends shooting down one of the spy planes and stating that it had violated Chinese air space, and then using that as casus belli for the war. This is never mentioned again, mostly because, thanks to a well-placed spy, China's opponents know exactly what they're doing.
- Crest of the Stars has a complex one. First is the destruction of the Gosroth with United Mankind insisting on setting up a joint investigation committee, with the suggestion that tensions are running high after the Abh annex the Hyde System. Ultimately subverted in that it is revealed that UM has been planning the whole thing for decades and on the Abh side Empress Ramaj sees right through it and refuses to play their games. She basically says "If you want a war then I will give you a war."
- Jingo is built around one - unsurprisingly, given the name. The excuse for war is a worthless island that's risen from the bottom of the sea after a volcanic event, almost exactly between Ankh-Morpork and Klatch. The two nations have been at peace for decades, but since the island would be such a useful launching point for an invasion if they did go to war, tensions immediately escalate over who gets to claim it - or as Vimes puts it, "we're supposed to go to war over some rock that's only useful if we have to go to war?" A more politically acceptable excuse to go to war and seize the island (the attempted assassination of a diplomat) had to be manufactured as a result. Fortunately, Sam Vimes wasn't fooled for a minute and set out to put a stop to it before things got out of hand. Carrot ended up arresting two entire armies for, among other things, Conspiracy to Commit a Breach of the Peace and buying enough time for Vetinari to swing a large number of trade concessions in return for ceding the island to the other side... about half an hour before it sinks again.
- In Small Gods, Vorbis arranges for one of his own church's missionaries to be murdered on his way back from Ephebe, then blames the Ephebians for killing the man and "counterattacks" with an army he'd sent out to cross the desert before the missionary had even visited their city.
- In Interesting Times, Lord Hong is giving extensive support to highly ineffective "revolutionaries" to create a pretext for him to launch a potent counter-revolution. As his long-term goal is to Take Over the World, he arranges for them to have a figurehead from outside The Empire (Rincewind), giving him an excuse to declare war on Ankh-Morpork in the future.
- The Dresden Files: In book 3, Grave Peril, this turns out to be the cause of most of the problems of the books: the Red Court was ready to launch a war against the White Council, and just needed a good excuse to do so, so they manipulate Harry into breaking Sacred Hospitality. Harry sees that he's being maneuvered into the trap and knows what the consequences will be, but since the alternatives would be the death of him and several innocents, along with the unmaking of a Holy Sword, he does it anyway.
- Only part of the Court wanted to go to war. The people behind the incidents of the novel wanted to make Harry suffer, figuring he wasn't crazy enough to trigger a full-on war... which he was. The more level-headed members tried to broker peace later because the war started before all their preparations were complete, preventing a quick victory for the Court.
- The manufacture of such a pretext is a major plot point in both the film and book versions of The Princess Bride.
- Mocked in the Star Trek: The Next Generation novel I, Q. The Q Continuum has a mortal enemy, the M Continuum. The Ms decided they wanted to go to war with the Qs. Why? Because there is something about them that pisses them off (their exact words). The Q Continuum requested a more eloquent reason. So one of the Ms insulted the mother of one of the Qs. This horrific affront (despite the fact that this Q, like all other Qs, didn't have a mother) could only be answered by a full scale war.
- Star Wars Legends:
- X-Wing: Isard's Revenge uses this for some Moral Dissonance. The New Republic is picking a fight with the neutral (if admittedly pro-Imperial) Ciutric Hegemony. Prince-Admiral Krennel is obviously not a nice man, but the best pretext the New Republic can come up with for starting the war is Krennel's execution of Sate Pestage several years previously when the latter tried to defect to the Rebellion, which at worst is a case of Kick the Son of a Bitch (Pestage was an Asshole Victim), along with Krennel's family (over a hundred people died in that purge alone) and a number of other purges he committed to keep himself in power. Myn Donos notes that one of his former squamates came from Toprawa, a planet deep within Imperial territory that's being repressed much more harshly than the worlds in the Hegemony due to its people's role in the theft of the Death Star plans, while even the generally saintly Admiral Ackbar more or less confesses that going after Krennel is as much about New Republic sabre-rattling to frighten bigger warlords like Teradoc as it about "liberating" the people under his rule (it takes place in the immediate aftermath of Grand Admiral Thrawn's invasion of the New Republic and the Republic brass doesn't want the remaining warlords getting ideas). And then things get muddled further when the New Republic stumbles upon a hidden lab that they claim proves that Krennel is trying to build another planet-killing superweapon, while Krennel claims that he never knew about the lab and it's obvious a New Republic trick to justify their actions. He's half-right: the lab is bait for the Republic by a clone of Ysanne Isard who is playing them and Krennel off against each other, and the superweapon indeed doesn't exist.
- Discussed in The Hand of Thrawn. A number of New Republic member states who are involved in the developing Civil War over the Bothans' role in the Imperial genocide of the Caamasinote only actually care about it because it gives them an excuse to pick a fight with historical enemies (the Diamalans and Ishori are one such example, and are introduced in the first book arguing about something else entirely).
- The Chiss are only allowed to go to war if provoked (i.e. the other guy has to shoot first), so developing a pretext for preemptive strikes is a veritable art form for the Chiss Expansionary Defense Force. The CEDF wanted to take out the marauding Vagaari for decades but the Vagaari wisely never attacked any Chiss worlds, so in Survivor's Quest they trick the Vagaari into attacking a Chiss diplomat (and the Skywalkers), then into hitting a major CEDF base. To drive home how seriously the Chiss take their Technical Pacifism, in the other half of the story, Outbound Flight, a young Mitth'raw'nuruodo intervenes in a fight between the main Vagaari fleet and the titular Republic ship (which he had orchestrated with the help of a Republic smuggler). Despite smashing them utterly with a handful of picket ships, he gets exiled for it.
- The Emperor's Coloured Coat by John Biggins. Otto Prohaska gets caught up in the plot to assassinate Archduke Ferdinand to create a pretext for war against Serbia. There are indications that the Austrian chief of staff is behind it, and he never finds out if the Archduke's death was part of the conspiracy or simply a lucky break by the assassins, who were so incompetent it was assumed they'd be caught long before they got near their target. Regardless, as the assassination triggers World War One and the break-up of Austria-Hungary, it turned out to be an even bigger cock-up.
- This is discussed several times in the mini-series Attila (2001). Flavius Aetius presents the young Attila's chief with one of his men who has been tortured as a pretext for taking on a rival tribe. Attila accuses Flavius of having inflicted the torture marks himself as they've been done post-mortem. Later after the chief dies, Flavius warns Attila that he needs a pretext before returning home to take on a rival, so Attila accuses him of murdering the previous ruler. After Attila creates the Hunnic Empire, he uses an earlier offer of marriage by the sister of the Roman Emperor (and half their empire as dowry) to invade their territory.
- Doctor Who:
- "Aliens of London"/"World War Three": The Slitheen try to gain access to Britain's nuclear arsenal and start World War III so they can sell the radioactive remains of the planet as fuel.
- "The Hungry Earth"/"Cold Blood": Alaya, the Silurian captured by the humans, actually tries to get killed in order to start a war between the two species.
- In the Frontier Circus episode "The Shaggy Kings", the renegade Indian Michael Smith tricks Ben and Tony into hunting buffalo on Cherokee lands, and then uses this an excuse to goad the Cherokee into going on the warpath.
- Murdoch Mysteries: In "Kommando", Major Cole ordered his squad to kill a British family in the Transvaal to stir up anti-Boer sentiment, before launching an unsanctioned attack on a Boer militia.
- In the 1996 mini-series Rhodes, Cecil Rhodes is planning to invade Matabeleland, currently ruled by the powerful Chief Lobengula. As he's short of finance, he intends paying his army of mercenaries and adventurers with a percentage of the Plunder (e.g. Lobengula's land and cattle) but fellow businessman Alfred Beit urges against this policy.
Beit: Tear these [contracts] up, for god's sake, and pay your men in cash! Have you thought what this means? The moment one volunteer signs this, there's no turning back. You've got to take Matabeleland. What happens if Lobengula won't play ball? What if he absolutely refuses to fight?! Are you going to take his country, his cattle, regardless? Never mind the British, you'll have the whole world against you.
Rhodes: Don't worry Beit, he'll play ball.
Beit: How can you be sure?
Rhodes: Because I'll push him, and push him until he does.
- Rome between Caesar and Pompey in Season One, and Marc Antony and Octavian in Season Two. Both cases involve Civil War, so it's important that those seeking war not be seen to incite it, as war against fellow Romans is more difficult to justify than war against foreigners.
- When the Romulans in Star Trek: The Next Generation aren't trying to destabilize other superpowers, they're trying to lure the Federation into making some blunder that would justify them making a first strike. They actually got pretty close with Picard and a traitor they were stringing along, but Picard hedged his bets and brought some Klingon backup, so they decided it wasn't worth the risk. Aside from the subterfuge being their hat, the Romulans go to such lengths because they don't want to be caught in a two-front war with the Klingons, who are allied to the Federation in this series and would provide assistance if the Romulans outright attacked.
- In The Hitchhiker's Guide to the Galaxy, it says that the history of warfare is divided into three phases: retribution, anticipation, and diplomacy.
- Retribution: Im going to kill you because you killed my brother.
- Anticipation: Im going to kill you because I killed your brother.
- Diplomacy: Im going to kill my brother and then kill you on the pretext that your brother did it.
- There was also the incident where two very tiny alien races were on the brink of war due to a Your Mom joke, but what really pushed both parties over the edge was a random comment made by Arthur Dent that traveled through space and time (which happened to be a deadly insult in one of their languages).
- In Shakespeare's Henry V, Henry announces to the French ambassador that the Dauphin's insulting gift of tennis balls will be repaid with war, but he has already proclaimed his intention to invade France immediately before the ambassador's entry — the Dauphin's insult just gives him an excuse.
- In Knickerbocker Holiday, Stuyvesant, Glorious Leader of New Amsterdam, believing that national greatness lies more in guns than butter, suggests that war with Connecticut could be imminent because, he alleges, the Connecticutans have had the cheek to build a fort on the Connecticut River.
- Played for Laughs in Civilization V with some leaders' war declarations. Mahatma Gandhi claims a couple of troops have gone rogue and attacked your border unprovoked, but don't worry, he's sent a Strongly Worded Letter kindly asking them to withdraw. Augustus Caesar on the other hand bluntly informs you that "My treasury is emptying and my soldiers are growing bored. Therefore you must die."
- Civilization VI introduced casus belli as an actual mechanic. Invoking one when declaring a war reduces the diplomatic penalties received for being a warmonger in the eyes of other civs. The reduction ranges from minor (being honest about commencing a hostile land-grab) to complete negation (reclaiming a declared ally's territory or liberating your own cities carries no warmonger penalty, even if you "technically" declared a new war to recover what you lost in the last one).
- In Dragon Age II, The Church controls all mages and has them guarded at all time by Templars, who will hunt any mage who tries to flee and kill those who show any signs of becoming vulnerable to demonic possession. Since demons offer powers that help a lot in escaping the templars, this actually happens quite frequently. With the templars taking less risks and even sympathising with those who try to escape being treated as being vulnerable to possession, things are constantly getting more dire for mages, but more moderate factions are always intervening to prevent a complete purge of all mages. In a desperate, though brilliant, move the mage Anders provides a reason for the templars to start a purge immediately without preparation, in the hope that it will unite the mages to fight for their lives, while there is still a chance they can win. He does that by blowing up the local main church with all its priests and publically admiting to the Templars that he did it. When the Templars than used that as an excuse to purge a Circle that their leader knew Anders was never a part of, the resulting outrage from the other Circles kicked off a full-scale war that would finally force the issue to be addressed.
- However, going with the game's Failure Hero theme, it didn't actually work. The rebellion didn't really spread beyond Kirkwall until a mad Lord Seeker tried to purge the Val Royeaux circle after a mage murdered a Templar, breaking away from the Chantry which had specifically ordered him not to in the process, in Asunder.
- Galactic Civilizations 2 has a random event where people from one civ automatically assassinate a very high-ranking politician of another civ, forcing war between the two.
- The Legend of Heroes: Trails in the Sky: As a small kingdom to the south with a pitifully small army and an abundance of Septium ore, Liberl made an easy target for the Erebonian Empire. Unfortunately for said empire, Civil unrest among the Reformist and noble factions left the government in a politically sensitive position. To tip the scales in their favor, a small village on the border named Hamel was mercilessly butchered down to the last man, woman, and child. The official story pinned it on Liberlian soldiers, but in fact were Jaegers in disguise. This is why several characters in the overall Trails series have plenty of trauma to go around as the handful of survivors to escape. A deciding factor that ended the war was the condition that no one on either side was to reveal the truth about Hamel as an act of truce. The climax of the Second Chapter'' reveals that the main villain Weisman whispered the name to select people to suggest the idea in the first place, which would give him the opportunity to mold whoever survived into the perfect slave for him to control.
- Used in Modern Warfare 2, where Vladimir Makarov, a major Russian extremist terrorist, perpetrates a massacre in an airport in the middle of Moscow while Private Joseph Allen, an American CIA agent, is planted in his inner circle. However, Makarov knows about Allen, and the Private is killed and dumped in the airport, and his body used as a pretext by the war-happy Ultranationalists to give them an excuse to invade the United States. The fact that as of Modern Warfare 3 Makarov appears to be covertly in control of the entire Russian military helped sell this.
- This trope is actually active on both the Russian and American sides in different ways. The Russians have been looking for an excuse to go to war with America for years, and are just waiting for a catalyst. Even if the US was completely uninvolved, there's a fairly decent chance they would have blamed the CIA anyway. Indeed, they may have done just that. A well known internationally wanted terrorist is seen, plain as day, strolling into an airport with a machinegun. Even though Allen's corpse is left there, the only thing that would identify him as a CIA agent (or even an American for that matter) is information being fed to the Russian government by a terrorist organization or the game's villain (who are both less than reputable).
- On the American side, this is also an example of the "hard-line elements from both sides co-operate with each other" example above, since General Shepherd, commander of the US Army Rangers and Allen's superior, was collaborating with Makarov to start a Russo-American war and planted Allen in Makarov's cell for the sole purpose of BEING the catalyst. All part of his plan to reinvigorate America's military might after the nuclear explosion that killed 30,000 Marines in the first Modern Warfare pacified it. Naturally, once the war actually kicks into gear Shepherd wastes no time turning on Makarov, while simultaneously trying to cover up that he was ever involved with him in the first place.
- Paradox Interactive's grand strategy games usually require you to come up with a casus belli (called a CB in fandom) before you can declare war on someone:
- In Crusader Kings you can have your Spymaster fabricate claims on a neighboring county to justify your expansion, while in Europa Universalis you can similarly find "obscure documents." At other times in EU or Victoria: An Empire Under the Sun, you might see border incidents like the pig one occur.
- In Crusader Kings II this is largely religion-dependent: Christians, Jews, and Mazdans need claims on titles (which can be faked) or holy war justifications to conquer territory (2.8 adds the "border dispute" casus belli, which costs resources to use and incurs an opinion penalty from other rulers). Muslims and pagans are free to declare wars for single counties without much consequence (especially Germanic pagans, who can target any coastal county).
- Stellaris has a range of casus belli based on a star nation's ethics and government type. Normal nations can declare wars of conquest only after spending Influence to stake claims to other empires' systems, while Pacifistic empires can only "liberate" worlds, creating a new nation with identical ethics to their own. You can also declare war to specifically humiliate a nation you've declared your rival, force someone to become your vassal, or impose your ideology upon them. Fanatical Purifiers, Driven Assimlators, and Devouring Swarms, on the other hand, don't really need a casus belli to attack a neighbor, and likewise other nations can use the "Contain Threat" justification against them. And just owning a Colossus is enough to justify another power waging total war against you, or vice versa.
- Star Control II reveals that the human-VUX First Contact failed not because the human captain off-handedly called his opposite number ugly, figuring the translators weren't working yet, but because the VUX find humans too ugly to let live. They simply used the "insult" as a pretext to prepare for war. They were conquered by the Ur-Quan and absorbed as Battle Thralls, which only worked in their favor.
- In Star Trek Online the Klingon Empire uses Undine infiltration of the Gorn as an excuse for stepping up their border war with them into a full-scale invasion, and later try to retroactively use the same excuse to justify attacking the Federation (even though they had openly admitted in the backstory that they were just after territory).
- One arc of Escape from Terra revolves around the United World trying to incite an incident on Ceres that they can use as a pretext for a second invasion attempt (first time they claimed Ceres was rebelling, the natives made it clear Ceres was never part of the UW in the first place). First a few covert ops soldiers go in and try to start a bar fight, but due to the Zero-Aggression Principle most Cereans follow that doesn't work. Then those guys buy a hotel and a small platoon of troops move in, but the locals just accommodate them. And as a last ditch the commissar took a twelve-year old girl hostage and told a prominent local to shoot one of her men disguised as a tourist or the girl would die. The Cereans instead brought out strippers to distract everyone until they rescued the kid, and the soldiers turned on their political officer.
- Imperium Nova has a feud system. When one House engages in actions against another House such as withholding taxes, insulting dynasty members, espionage (and are caught), or attacking facilities; the offended House gains feud points that can be spent attacking the offender. If a House attacks another House, on a planet under Imperial Jurisdiction, without feud the Emperor declares them a Renegade, which allows every other House to attack them with impunity.
- In Mahu's "Second Chance", the Galactic Commonwealth's many wars each start with a different pretext. From stopping the genocide of a whole race at the hands of fanatics, to stopping the expansion of an ever-hungry Hive Mind, the Commonwealth never goes to war without reason. However, it is also argued by some of the nation's neighbours and rivals that these reasons sometimes just look like convenient excuses to expand the nation's frontiers and gain more resources.
- In the New Deal Coalition Retained timeline, a firefight at the inter-German border in 1988 — caused by overzealous West German guards stepping in when the East Germans execute refugees attempting to flee across the border — serves to set off the powder keg that international relations have been ever since the December Coup, sending the world spiraling to World War III. Which is what the hardliners in Moscow want, as they see war as the only way to revitalize their economy. Hence why they sabotage diplomatic efforts to soothe matters by giving demands they know the West will reject.
- A few years after WWIII's end, a skirmish along the border between the Chinese and Japanese occupied regions of Manchuria is seized upon by General-Secretary Li Peng as an excuse to act on his anti-Japanese policies and go to war with them. Despite the propaganda spouted about it, absolutely no one is fooled about the actual reasons for the war.
- A South African state police force chasing Lozi separatist terrorists is drawn into a firefight with an Entebbe Pact peacekeeping force at the Lozi (formerly Zambia) border, leading to a tipping point in the escalating tensions between the Pact and the French Concordat-aligned nations of Africa, triggering an all out war.
- The ceasefire among the various factions in the Brazilian Civil War is broken when a commercial plane from the Estado Novo portion of the country is destroyed, apparently by a rocket launched from Republican-held territory, leading to the Estado Novo declaring war on the Republicans. In response, the Communists and Amazonian militants come to the Republicans defense, and soon other South American countries are also entering the war on both sides.
- World War II:
- The German justification for their invasion of Poland stemmed from, among other causes, False Flag Operations by German operatives designed to look like Polish aggression against Germany.
- Belgian King Leopold III tries to avoid giving Germany a reason to invade by refusing to allow British and French forces to take positions inside neutral Belgium during the "Phoney War".
- The Soviet-Finnish Winter War begins on the pretext of an artillery attack by Finns against the Russian village of Mainila despite Finland having withdrawn its artillery from the border to prevent such an incident.
- That pig thing, in the trope discription? It was real. It wasn't much of a war though: "The pig was the only casualty of the war, making the conflict otherwise bloodless." from The Other Wiki. The situation was diffused largely because the commanders of both sides flatly refused to fight over something so stupid.
- The War of Jenkins' Ear. The British had managed to get themselves exclusive rights to trade slaves in the Spanish colonies in America, but at the cost of Spanish crews being allowed to board British ships and search their cargo. Relations became rather strained, and then a one-eared merchant captain by the name of Jenkins showed up in Parliament with a severed ear and a story of Spanish brutality that sparked the above war. It is doubtful as to whether the ear exhibited in Parliament was actually Jenkins' lost ear, as historians today and his contemporaries believe that he lost his ear in a bar fight years before.
- World War I. The assassination of the heir to the Austro-Hungarian throne, Archduke Franz Ferdinand, by Serbian terrorists sponsored by the head of Serbian military intelligence to further the goal of Serbian dominance of the Balkans was used as an excuse to take down Serbia's racist military Junta and replace it with a government which didn't sponsor terrorists (even during the war there was no question of annexing Serbia, as doing so would only have added to Austria-Hungary's domestic political problems). Which sounds a bit unreasonable until you realise that the very existence of Serbia (an independent nation-state of ethnic Serbs whose sole foreign policy goal was to unite all the lands inhabited by Southern Slavs into Yugoslavia, which they envisioned as as a Greater Serbia) terrified the German/Hungarian elites that ruled the mindbogglingly multi-ethnic Austria-Hungary. Right from the start they thought that, with Germany backing them all the way, Russia would back down rather than risk war with them and Germany at the same time, just like six years earlier over the formal annexation of (Habsburg-occupied, technically Ottoman) Bosnia.
- For reference, the main ethnic groups in Austria-Hungary were, roughly by population: Germans, Hungarians, Czechs, Poles, Ukrainians, Croats, Slovaks, Serbs, Slovenes, and Italians. Plus a lot of Jews, most of whom spoke German/Yiddish or Hungarian.
- Furthermore, right from the start the German High Command's accepted plan of action was to use Aufmarsch I West (formerly Aufmarsch II West), deployed 80% of the army in the west to invade France through Belgium and attempt to encircle a large part of the French Army on French territory (failing that, they'd still end up occupying economically important French territory). So when Russia mobilized its armies Germany delivered an ultimatum to France as a pretext for war, demanding its neutrality despite being an ally of Russia and asking it to temporarily surrender fortresses integral to France's defenses (Verdun and Toul) along their shared border within 24 hours. The French didn't respond but mobilised the next day, as did the Germans; since about 1911 the Revanchism movement, a movement seeking revenge for France's defeat in the Franco-Prussian War and the re-annexation of the province of Elsaß-Lothringen (Alsace-Lorraine) had become a dominant force in French politics and was not to be denied. More importantly the French felt that this was an excellent time for a war: deadlock in the German and Austrio-Hungarian parliaments meant they hadn't increased their military spending and thus capabilities to match the 1905-1914 Franco-Russian increases, but that was set to change in the near future. Moreover the French did not feel they could count on Russian support in a war that mostly or only involved French (and not Russian) interests. Serbia was a cause that Russia was willing to fight for, and the French might not get another chance like it again.
- Or to make a long story short, a bunch of people wanted some stuff and threatened to go to war if they didn't get it, but mostly wanted a war. Some other people didn't want to give it to them but kind of wanted a war too. One thing led to another and there was a war, which everyone thought would be over in about three months (with their side victorious, of course). And then it snowballed into a really, really big war. Then about six months later, they all thought to themselves, "Why the hell did we do that?" But by then, they were committed.
- The Mainila incident, which the Soviet Union used as a pretext for invading Finland during the Winter War. It has been established that there is no way the Finns could have been responsible, as none of their artillery was in range at the time. See False Flag Operation.
- A few months later, the Soviets started claiming that the Baltic states captured and are torturing some of their soldiers. Remembering Finland, all three countries agreed to join the USSR. No attempt to find the captive soldiers followed.
- Similarly, the Gulf of Tonkin incident, in which an American ship on patrol claimed to have been attacked by Vietnamese gunboats, serving as a pretext for The Vietnam War; but the reports may have been fabricated to gain popular support for escalating military operations in Southeast Asia.
- It's a little more complicated. There were actually two "Gulf of Tonkin" incidents, separated by around 48 hours. The first incident took in disputed waters, claimed by North Vietnam as its territorial waters but by the US as international waters, conveniently not too far from an area where a South Vietnamese covert operation against the North was taking place. (North Vietnam claimed that US warships were supporting it, while US has denied it.) During this incident, which was very real, North Vietnamese patrol boats took the worst of it, while US warships suffered nothing more than a few dents. The second incident took place in the middle of night, roughly 40 hours later, in undisputed international waters. Sailors onboard US warships (which were involved in the first incident) thought that they were under attack by North Vietnamese and spent most of the night shooting at something...or nothing. Military intelligence officials who received the report thought the whole thing was a mistake by confused sailors and no actual attack took place—which has been confirmed by every investigation thereafter by military, government, academics, etc. But Johnson administration decided to ignore the intelligence report and assert that the second attack was real to justify escalating conflict.
- To make a trifecta, the sinking of the USS Maine in Havana Harbor provided America with the perfect excuse to start the Spanish-American War and take over Cuba and Spain's Pacific possessions. Investigations since then seem to be split on whether it was a deliberate act of war by the Spanish, a False Flag Operation by Cuban rebels, or a genuine accident caused by a fire in a coal bunker.
- It didn't help that the American press was actively encouraging war with Spain by citing (false) Spanish atrocities. Why? To increase their sales figures.
- Another False Flag Operation was the Mukden Incident of 18 September, 1931, in which the Japanese officers faked an explosive attack on the South Manchurian railroad to spark off the Manchurian Crisis.
- Another escalation of the Japanese war in China start with a Japanese soldier peeing in the woods. Seriously - he missed role call after training while taking a leak, and his commanding officer challenged a nearby Chinese patrol, thinking the man might have been abducted or attacked by the Chinese. Tempers flared and somebody (from which side is not known) opened fire. Things were nearly smoothed over by the local commanders, but the Japanese Army high command refused to de-escalate as they had been looking for any old pretext to expand into more of China anyway.
- The revolution that led to the Republic of Colombia becoming independent was supposedly triggered by "El Florero de Llorente" (the vase of Llorente), which was a trick by the supporters of the independence to upset a Spanish merchant and incite the crowd against the Spanish people. This led to a popular expression used when you need a excuse to start a fight.
- The Gleiwitz Incident was used as a pretext for Germany's invasion of Poland in 1939. An SS commando in Polish uniforms attacked a radio station near the Polish border and broadcast anti-German propaganda. They even dressed a prisoner in Polish uniform and shot him to add authenticity.
- It was actually bigger than people think. During the summer of 1939, the Nazis staged attacks on ethnic Germans in Poland, claiming this was the work of Polish terrorists.
- The Football War had a football match as part of its pretext.
- Lampshaded in the Great Louisiana Maneuvers of 1941. These were held to prepare the US Army for the widely expected entry into World War II and in a way marked the beginning of the United States as a superpower. Two trumped up factions called the Red Army and the Blue Army were set to test their prowess against each other. To begin the contest it was decided that they represented two nations fighting for control over the Mississippi River.
- There's a conspiracy theory that 9/11 was a False Flag Operation by the Bush administration in order to provide a pretext for invading Iraq. Leaving aside the part where the whole thing started life as a work of fiction, the correct response for someone too bored to counter with hard data is to invoke the names of Occam and Hanlon.
- False Flag Operation aside, there is compelling evidence to suggest that 9/11 was used to justify a first-strike in Iraq for reasons varying from personal (such as removing Saddam Huessein from power) to financial (such as taking all of Iraq's oil and getting filthy rich).
- 9/11 aside, the main pretext for war as sold to the public was the Iraqi government failing to hand over it's hidden chemical weapon stockpiles. Weapons it would later turn out they did not actually possess.
- An alternative conspiracy theory holds that al-Qaeda were the perpetrators, but claims the government knew the attack was coming and did nothing to gain an easy pretext. Another unrelated theory says Franklin D. Roosevelt was aware of the impending Pearl Harbor attack and let it happen for the same reason.
- The Crimean War started thanks to a dispute between Catholic and Orthodox clergymen in Bethlehem (present-day Israel, then part of the Ottoman Empire), over the keys to the Church of the Nativity. This led to the awkward situation of Catholic France and Anglican Britain siding with Muslim Turkey against Orthodox Russia over a religious argument.
- In the runup to the Six Days War, Nasser was either intentionally provoking Israel or blustering to look tough. First he called for an end to the UN mission acting as "buffer" between Egypt and Israel in the Sinai, then he started mobilizing troops, ostensibly in preparation for war - all while saying stuff like "We'll destroy Israel" on the radio - and ultimately, he closed the Straits of Tiran,note which Israel had repeatedly said would be grounds for war. Guess what happened?
- In perhaps one of the most poorly thought out attacks in history, the Japanese attack on Pearl Harbor during World War II was intended to scare the US into remaining neutral rather than joining the Allies. Of course, the US had been aiding the Allies with supplies for years at that point and had been desperately searching for a reason to justify entering into the war in a military capacity. This was less about justifying it internationally — the other Allied forces were happy to have the US join the fight and would not have complained regardless of the pretext — and more about justifying it domestically, since public opinion within the US was fairly split about whether they should enter the war. Then the Japanese attacked and any resistance to joining the war evaporated as now it would look worse NOT to retaliate.
- When Germany declared war on the United States a few days after Pearl Harbor, Hitler held a speech where he recapped a long list of alleged or real American aggressions and war crimes against Germany and her Axis allies in the previous years. His main complaint was that the US Navy had attacked German naval and merchant marine vessels several times in the months prior to Pearl (which was actually true). The complete list of casus belli he invoked can be read here.