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Pretext for War

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He messed with the H.R.E. - Casus Belli.
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!

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 Rage Breaking Point 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 "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" or even "because we're afraid of you"; 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.


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    Anime & Manga 
  • 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.
  • 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.
  • Fairy Tail: Jose Porla, the leader of the Phantom Lord guild, was tired of being Always Second Best to Fairy Tail, and he was eager for a job to come up that would give him an excuse to fight them. So when Lucy's rich father hires Phantom Lord to bring her home, he doesn't merely kidnap her but also commits increasingly extreme acts of violence against Fairy Tail in order to goad them into a conflict that would culminate in Fairy Tail and the town it resides in being wiped off the map.
  • In Overlord, when the Sorcerer Kingdom's Too Dumb to Live Unwitting Pawn attacks and pillages a convoy they had sent with humanitarian aid for the Roble Holy Kingdom, Ainz ditches his original plan of destabilizing the Re-Estize Kingdom before vassalizing them and uses the incident as an excuse to declare war against them instead.
  • 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.
  • A heroic example occurs in Yu-Gi-Oh! ARC-V, with LDS (Group A) taking advantage of the team from Academia (Group B) going to Miami 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 Magitek 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.

    Comic Books 

    Fan Works 
  • After That Fateful Night: The griffons decide to invade Equestria after Nightmare Moon takes over, citing Princess Celestia's disappearance as their primary reason for doing so. This actually convinces the remnants of the royal guard to join forces with them.
  • Code Prime: Despite their alliance, many of the lower-ranked Decepticons are eager to wage war with the Earth, irritated with the Holy Britannian Empire's Fantastic Racism and inefficiency. Once Megatron learns about the Ragnarok Connection, he launches a full-scale invasion.
  • 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.
  • Equestria Total War: The Gryphons justify their war against Equestria by deeming the ponies' control over nature to be blasphemous and fundamentally immoral. At one point, Derpy learns that this pretext is so thin that even in their own armies, no gryphon who holds a rank higher than lieutenant actually believes in their supposed cause.
  • Faith in Superior Firepower: After the Bright Foundation loses one of their science outposts to hostile wildlife, they establish a colony on that same planet in order to justify assigning and deploying a large amount of military and special forces units to the area, all to protect their scientific investments under the pretense of protecting the colony.
  • Fallout: Equestria: "The Littlehorn Massacre" was the primary reason for the war between the zebras and Equestria, especially with the return of Princess Luna. The zebras were highly superstitious and terrified of Luna, due to her close association with the stars and night, which the zebras believed were evil. Celestia, Luna's sister and ruler of Equestria, built her sister a school at the edge of Equestria to help her get out of the Gilded Cage that Celestia had unintentionally created. This location was close to zebra land, and things were already strained due to trade talks and arguments over resources. When a zebra refugee convoy passed too close to the school one night, the school faculty panicked and activated their defenses, wiping out the convoy. One of the survivors was a zebra commando, who slipped into the school grounds and unleashed a chemical weapon that killed everyone, faculty and students alike. The "Littlehorn Massacre" destroyed any possibility of peace between the two countries. Celestia felt so much guilt over having built Luna's school at Littlehorn in the first place that she stepped down as ruler of Equestria and gave the throne to Luna. And, once again, because the zebras viewed Luna as basically the Antichrist, this made everything even worse.
  • What About Witch Queen?:
    • The final reason for Arendelle and Weselton to go to war is a 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 a war between Isles and Arendelle by killing Anna and making it look as if it's Islanders' fault.
  • Your Heart a Haven of Thorns (Naruto) has a Justified version: Summoned beasts take contracts very seriously, a fact Enma once exploited in order to trick the Tiger clan into a terrible deal involving the death of an innocent cub. Ever since then, the Tiger clan have been looking for an opportunity to enact their revenge; however, Enma's father has been careful to ensure that the Tigers have been unable to find any further fault with the Monkeys. Then Enma's summoner Hiruzen, unaware of all this, inadvertently provides the Tigers with just the sort of excuse they were looking for...

    Films — Live-Action 
  • 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.
  • 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 of The Emperor and the Assassin is about this—Ying Zheng seeks to conquer all of China, and needs a pretext to attack the state of Yan. So he sends the Lady Zhao to convince the King of Yan to send an assassin to kill him, to stop this invasion from taking place.
  • 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. Saladin would come to regret waiting for it, since Reynald went with "murder Saladin's sister" as his provocation.
  • 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 Outlaws IS Coming!, Rance Roden is attempting to hunt the buffalo into extinction to goad the Indians into war, and allow him to make a profit selling arms to the Indians and eventually seize control of the US west of the Mississippi.
  • The Princess Bride has this as its entire plot: the men who kidnap Buttercup are doing so in order to start a war between Florin, her home country, and their enemy of Guilder. The plot is masterminded by her fiancé Prince Humperdinck; after Vizzini's kidnapping plot is foiled, he decides to personally murder her on their wedding night, saying that it'll work even better.
  • 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.
  • Star Trek VI: The Undiscovered Country:
    • The movie features 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 has been 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 creating a political crisis that ousts the current Chancellor and lets him claim the seat as a popular champion for reform against obstructive bureaucracy.
    • In Attack of the Clones the Clone Wars are sparked when revelation that the Separatists have built a secret army of droids on Geonosis prompts the Republic to deploy the recently discovered clone army grown on Kamino, despite the shady and unknown details of their secret commissioning years earlier. Of course, both these armies were built by Palpatine's design and the war itself is just a pretext to seizing control and turning The Republic into The Empire
    • Which comes to fruition in Revenge of the Sith, when he completes his takeover by luring the Jedi into coming after him directly and trying to kill him. He decries it as an assassination attempt and a failed coup d'etat on their part, all the justification he needs to brand every Jedi a traitor and mark them for death just as he orchestrates victory in the civil war declares himself Emperor.
  • In the 1982 political satire Wrong is Right, 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.

  • 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."
  • Discworld:
    • 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, Omnia declared war on Ephebe in retaliation for the murder of an Omnian missionary... well, the mocking and humiliation of an Omnian missionary who was later mysteriously murdered on his way home, but the fundamental truth is that the Ephebians murdered the missionary by not embracing his preachings. While this led to a Curb-Stomp Battle that sunk the Omnian fleet, Exquisitor Vorbis made the most of the situation, by sneaking an Omnian army - that had begun crossing the desert before the missionary even entered Ephebe - into the enemy capital during peace talks. "You had to have a mind like Vorbis' to plan your retaliation before your attack."
    • 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 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 Otto 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.
  • Mocked in The Elenium, when a discussion on whether to go to war with Otha and his Zemochs could be justified. It’s brought up that there was never an armistice or even a declared ceasefire, just the fact that both sides bludgeoned each other to exhaustion that led an end to the overt hostilities. One of the Church Knights jokes that the Eosian continent was just resting, for 500 years, and that they felt sufficiently rested to resume the fight.
  • Fire & Blood: Aegon the Conqueror had already been planning on taking Westeros one way or another, he and his sisters having scouted out much of the continent beforehand, but it's only when his offers of dynastic alliance are violently rebuffed that his family bring out the dragons, and set about taking it by force.
  • How a Realist Hero Rebuilt the Kingdom:
    • A multilayered one in volumes 2-4. Main character Souma Kazuya, the summoned hero-turned-King of Elfrieden, baits the antagonistic neighboring country of Amidonia into aiding the other side in an uprising against his rule by corrupt nobles. Amidonia is itself using the Civil War as cover to retake some of the territory they lost to Elfrieden in a war two generations earlier. Souma defeats them and occupies their capital, and deliberately makes himself look good to the citizens compared to the ultra-militaristic Amidonian royals by investing in their arts and culture, the goal being to make them long for him to come back after he withdraws and give him an excuse to occupy that part of the country permanently. He miscalculates slightly: Princess Roroa of Amidonia orchestrates a nationwide uprising that forces her brother Julius to flee the country, and then betrothes herself to Souma to unite them into the United Kingdom of Friedonia.
    • Subverted in volume 13. Souma gets into a conflict with the Nine-Headed Dragon Archipelago Union over fishing rights, and spends several months with foreign propagandists trumpeting to the fiercely independent islanders about how he's coming to attack them, with the fishing dispute as the pretext for invasion. The war itself was the actually the pretext for a Genghis Gambit he arranged ahead of time with the Nine-Headed Dragon King, Shana, who used it as an excuse to get the islands' fleets to marshal in one place after their terminally fractious chiefs couldn't agree on a plan to deal with the root cause of the problem—a kaiju named Ooyamizuchi—as well as give Souma's heavier naval vessels an excuse to be there to help.
  • 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 : 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 Pay Evil unto Evil (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 squadmates (in Aaron Allston's Wraith Squadron books) 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. 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 Caamasi 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 Driving Question of the book is, in the event the specific collaborators cannot be identified, is it justifiable to hold the entire Bothan state/species responsible?
    • 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.

    Live-Action TV 
  • 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 chief. 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:
  • 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.
  • The very first scene of Star Trek: Discovery is a Klingon warlord speechifying to his followers that The Federation is a threat that must be destroyed. It's part of a Genghis Gambit to unite the feuding houses against a common foe. He gets his wish in the next episode when open war breaks out.

  • In The Hitchhiker's Guide to the Galaxy (1978), it says that the history of warfare is divided into three phases: retribution, anticipation, and diplomacy.
    • Retribution: "I'm going to kill you because you killed my brother."
    • Anticipation: "I'm going to kill you because I killed your brother."
    • Diplomacy: "I'm 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).

    Tabletop Games 
  • In the Warhammer Dark Fantasy universe, Gelebor II, a High Elven King, got into a disagreement with Gotrek Starbreaker, the High King of the Dwarves, over attacks on Dwarven trading caravans at the borders of Ulthuan, the High Elven homeland, that were actually carried out by Dark Elves seeking to inflame tensions between them to the point of war. When Gelebor denied all involvement in the attacks and refused to investigate, Forek Grimbok, one of the Dwarven ambassadors sent to Ulthuan, threatened to hold the entire court of the High Elves responsible if they could not find who among them was responsible, Gelebor got angry and, seeking to preserve his reputation, ordered Grimbok's beard shaved off before throwing him out of Ulthuan. This act was a grave insult to not only Grimbok, but the High King and the entire Dwarven race by extension, and proved to be the Last Straw. The resulting war, which devastated both sides of the conflict, was called the "War of Vengeance" by the Dwarves, but was called the "War of the Beard" by the Elves. It's not advisable to call it by the latter name within dwarven earshot.

  • 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.

    Video Games 

By Creator:

  • Paradox Interactive's grand strategy games usually require you to come up with a casus belli 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, Devouring Swarms and those who Become the Crisis, 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.

By Series:

  • Age of Wonders: Planetfall and Age of Wonders 4 both use war justification as a game mechanic, called Casus Belli in Planetfall and Grievance in 4. Actions like trespassing in another nation's territory or snatching up territory on their borders will generate points. It's also possible to spend resources to fabricate a pretext for war. Declaring war without justification causes both economic and diplomatic penalties, as neither your own citizens or other rulers are happy with a warmonger. Conversely, declaring war with high justification grants temporary bonuses. An ally requesting you declare war on their enemy always grants a large amount of Casus Belli / Grievance.
  • Civilization:
    • 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 (declaring a new war to liberate cities, your own or an ally's, carries no warmonger penalty on its own).
  • 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.
  • Dragon Quest III: One of the Personality-determining scenarios players of the remakes can be presented with is a kingdom that is on the verge of war, courtesy of the Queen convincing her husband that another land has been scheming against them. The hero overhears the Queen gloating to herself that she made the whole thing up because she coveted the jewelry the other kingdom's queen owns. The player must then decide what, if anything, to do with this information.
  • In Fire Emblem: Awakening, King Gangrel of Plegia abducts a Ylissean noblewoman he (falsely) claims intruded over his border and uses the deaths of his own soldiers in the rescue attempt as a loose justification for a war of aggression. Everyone present can see it's a total farce, he just needed enough plausible deniability to keep their mutual northern neighbour coming down on him like a ton of bricks.
  • 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.
  • Humankind has a more abstract form of this in its War Support. Grievances against other empires aren't themselves a valid pretext, but if demands for reparations go unmet, it builds public support for war. Notably, this also works the other way. When war support hits zero during a conflict, that side is forced to capitulate, and gets no say in the terms.
  • Mass Effect: Andromeda: The kett initially made peaceful diplomatic overtures towards the angara, then abducted or attacked many of their leaders, claiming the angara fired first. The angara were too busy arguing with one another to notice the holes in the kett story until it was a little too late.
  • 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.
  • 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).
  • Trails Series:
    • 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 a handful of survivors managed 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 Weissman 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.
    • The Legend of Heroes: Trails of Cold Steel: Despite the games taking place in Erebonia, the nation responsible for the burning of Hamel, the truth of the incident isn't discussed until the third game, which gives more insight into why the incident happened. Commoners were rising up in rank in the Imperial Army, and nobles in the army weren't okay with that. These nobles are the ones Weissman convinces to attack Hamel as a pretext for the Hundred Days War, which they could brag about as an achievement. Gilliath Osborne, a leader in the Imperial Army and one of the commoners despised by those nobles, warns them to not attack Hamel. In response, they hire jaegers to attack his home, leading to the death of his wife and his son Rean being mortally wounded. The only reason Rean doesn't die is because Osborne makes a Deal with the Devil to save his son's life. Osborne is the one who negotiated with the queen of Liberl and managed to stop the war under the condition that everyone who knows about Hamel keep quiet about the truth. The way Osborne managed to deal with the Hundred Days War won him the trust of Emperor Eugent III, who responds by making him the first commoner-born chancellor in Erebonia's history. This serves as the Start of Darkness for Osborne, who would go on to become the Evil Chancellor and Big Bad of the Cold Steel games.
    • In the third Cold Steel game, Emperor Eugent is shot by a survivor of Hamel. Osborne uses the fact that the gun was from Calvard as a pretext to declare war against them, something anyone with half a brain knew he'd been prepping for for at least a year.
  • In Triangle Strategy, Dragan's death as part of a False Flag Operation is used by Gustadolph as a pretext for the Aesfrosti to invade Glenbrook and take control of the Grand Norzelian Mines.
  • In War Pips you, the general of the Piponian invasion force, are tasked with "liberating" the Oiyelistan people from their petroleum reserves and their unholy custom of putting water on their cornflakes instead of milk.

  • 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.

    Web Original 
  • 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 tried to avoid giving Germany a reason to invade by refusing to allow British and French forces to take positions inside neutral Belgium during the "Phony War". It didn't work — Hitler invaded Belgium and the other Low Countries anyway in 1940 in order to clear the way to invade France by using the Ardennes Forest and the French/Belgian border to bypass the Maginot Line along the French/German border.
    • The Soviet-Finnish Winter War began 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.

    Western Animation 
  • In Dragons: Riders of Berk, Dagur the Deranged visits Berk, having heard a rumor that they have taken to training dragons. It is heavily implied that Dagur wants to use that fact as an excuse for the Berserker tribe to wage war on Berk as he has his entire armada just offshore.
  • A Thousand and One... Americas: Near the end of the seventh episode, it is revealed that Balam faked the theft of a sacred mask to frame a neighboring tribe in order to start a war against them and eventually conquer them. Chris, Lon and a friendly priest manage to retrieve the mask and expose Balam's sordid plan before anything terrible happens.

    Real Life 
  • That pig thing, in the trope description? 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 defused 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" (actually a group including Serbs, Croats and Bosniaks, but authorities painted the plot as entirely Serb-run) 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), deploy 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.
  • 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. 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.
  • 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. Not that there weren't perfectly real atrocities being committed by Spain in its attempt to suppress a Cuban Revolution— including the first documented use of what the Spanish called "Campos de Concentración". Unlike the later (euphemistic) use of the term by the Nazis, those were supposed to be "only" internment camps to hold the civilian population in order to deprive the guerillas of support. They were however guarded by armed Spanish soldiers, had barbed wire, and (due to military corruption) were insufficiently provisioned and disease-riddled, leading to horrific death tolls— even if the claim that it was due to incompetence or carelessness rather than a deliberate policy of murder is somewhat more credible than in later cases. Only a few years later, the same American public who had been outraged at that treatment of the Cuban civilian population didn't care in the slightest about the very similar methods the US used to suppress the uprising of the Filipino population (the Phillippines having been acquired from Spain as a result of the war).
  • 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 started with a Japanese soldier peeing in the woods. Seriously — he missed roll 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 team in Polish uniforms attacked a radio station near the Polish border and broadcast anti-German propaganda. They even dressed a prisoner in a Polish uniform and shot him to add authenticity. Even before that, during the summer of 1939, the Nazis staged attacks on ethnic Germans in Poland, claiming this was the work of Polish terrorists. This allowed Hitler and the Nazis to paint their invasion of Poland as an act of self-defense. Nobody outside Germany bought it, with France and the United Kingdom declaring war on them within a few days.
  • 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 their 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 Hussein 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 its hidden chemical weapon stockpiles; it was later determined that no such stockpiles existed.
    • 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 that either Franklin D. Roosevelt or Winston Churchill 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, Anglican Britain, and the Catholic but anti-Pope Kingdom of Sardinia siding with Muslim Turkey against Orthodox Russia over a religious argument. They had the very open goal of unifying Italy, which would necessarily include annexing Rome (as no Italian would accept another city as capital except as a temporary measure), and since the reigning Pope was opposed to a federation, that meant Sardinia would eventually go to war with the Pope.
  • 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 (Israel's only access to the Red Sea and of crucial importance for Israeli trade with Asia), 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. However, the idea that it was meant to "scare" the US is historically suspect. Pearl Harbor was far from the only objective; coordinated attacks over the course of a few hours (all at local dawn) basically swept Allied forces from the Pacific in a single stroke, including taking the US territory of the Phillipines and eliminating American air power in the Pacific with it.
  • 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.
  • Pennsic, the Society for Creative Anachronism's annual simulated-warfare camping event, got started when Cariadoc of the Bow declared war on himself. While serving as King of SCA's kingdom in the Midwest, he sent a challenge to war to the then-king of the Eastern seaboard, who laughed it off. Not long after, Cariadoc moved to the East coast in Real Life, where he ascended to become King of the East; a new incumbent was elevated to "rule" the Midwest. Digging up the challenge he'd previously issued, he feigned outrage at the taunts he'd written himself, raised the call to "War" against his former kingdom, mustered his forces to battle those of his Midwestern successor at the border in western Pennsylvania... and lost.
  • The ancient Romans believed their gods looked unfavourably at wars of aggression. Somehow, over the centuries, they were provoked by hostile neighbours - or aiding their beleaguered allies - into conquering their way from a single city to an empire spanning over several continents. The Punic Wars are a good show at what Rome would lower itself to in pursuit of a pretext:
    • The First was caused when the Mamertines, mercenaries that had previously worked for Syracuse, occupied the city of Messana (modern day Messina) and requested help from both Carthage and Rome. Carthage acted first, pressing Syracuse into letting the Mamertines go and garrisoning Messana, at which point the Roman Senate, which had been aiming to expand in Sicily for a while, decided to not go to war, as Carthage was an ally, and the request was already sketchy to begin with, due to the Mamertines having stolen the city from its rightful owners to begin with... Then warmongers in the Senate put the decision in front of the Centuriate Assembly, the one organ that, as the popular assembly, had more power than the Senate and held out the prospect of plentiful booty, at which point the merchants that would benefit from said booty decided to accept the request, much to Carthage's rightful indignation.
    • After Rome won the First War, Carthage's influence zone in the Iberian Peninsula was limited to the area south of the Ebrus river... And then Rome made an alliance treaty with Saguntum, a prosperous and well fortified city right in the Carthaginian influence zone. A few years later, Hannibal, knowing that Saguntum would be an enormous threat, conquered it, and Rome declared war.
    • After losing the Second Punic War, Carthage was banned from declaring war on anyone without the permission of Rome, a ban that the Romans considered eternal unless a new treaty said otherwise but the Carthaginians considered bound to expire as soon as they had paid the enormous war indemnity. Thus Carthage did not react to Numidian aggression for fifty years, begging Rome for redress or at least permission to counterattack the whole time, and only raising an army after they paid the indemnity and thus considered the treaty expired. The Numidians crushed the Carthaginian army at Oroscopa, and the Carthaginians, realizing the Romans did not consider the treaty expired, executed their general as penance and sent embassies to effectively beg for forgiveness, but Rome, who didn't want the commercial competition and had factions that used Carthage as a political boogeyman, eventually declared war. When the Romans arrived at their African allied harbor of Utica, Carthage sent a last embassy, to whom the consul Censorinus demanded they handed over all weapons. Carthage brought to Utica all their weapons and their military fleet just to stay on the safe side... At which point Censorinus demanded the Carthaginians relocated 16 km away from the sea. The Carthaginians recalled their ambassadors and started rebuilding their weapons and ships, and the Romans attacked.
  • When Russia invaded Ukraine in 2022, they claimed it was to stop NATO eastward expansion... except Ukraine was not in the process of joining NATO, only sending in an application after Russia annexed four occupied oblasts. On top of that, NATO had never made any official binding agreement not to expand eastward, despite repeat claims by Russian propaganda that they had. Then they claimed it was to de-Nazify Ukraine... except Ukraine's president is Jewish and far-right parties have minimal support, and neo-Nazis were seen among the Russian invaders (though non-Russians are far more likely to call bullshit; Russia's Propaganda Machine heavily downplays the Nazis' antisemitism, instead defining the Nazis purely by the fact that they invaded the Soviet Union and by extension Russia, and apparently extending that to mean all opponents of the Russian Federation are Nazis). Then they claimed it was to stop Ukraine from gaining nuclear weapons... which they weren't. Later, they claimed it was to "de-Satanize" Ukraine... except 87.3% of Ukrainians identify as Christian, largely Orthodox. Needless to say, Russia has yet to provide a halfway convincing reason for invading. Ironically, both Sweden and Finland quickly announced their intention to join NATO shortly after the war began.

Alternative Title(s): Excuse For War, Casus Belli