[[quoteright:300:[[UsefulNotes/WorldWarII http://static.tvtropes.org/pmwiki/pub/images/USSArizona_PearlHarbor.png]]]]
[[caption-width-right:290:''"Yesterday, [[UsefulNotes/WorldWarII December 7, 1941]] — a date which [[ThisIsUnforgivable will live in infamy]] — the [[AwakeningTheSleepingGiant United States of America was suddenly and deliberately attacked]] by naval and air forces of the [[UsefulNotes/ImperialJapan Empire of Japan]]."'' - UsefulNotes/FranklinDRoosevelt]]
->''"Of course you know [[TropeNamer this means war!]]"''
-->-- '''[[Creator/TheMarxBrothers Groucho Marx]]''', [[WeirdAlEffect then]] '''Characters/BugsBunny'''

%% One quote is sufficient. Please place additional entries on the quotes tab.

Now you've done it.

A declaration that someone has broken the last straw, crossed the MoralEventHorizon, hit the BerserkButton or otherwise gone too far. The person making this declaration will now commit themselves to unleashing every ounce of asskicking they have at you until they get their way, and will not allow anything to stop them.

If the offended party is a KarmicTrickster, expect much {{Slapstick}} to follow. The Japanese have a specific cultural sub-trope and StockPhrase for this: ThisIsUnforgivable. May lead to a character exhibiting CrouchingMoronHiddenBadass, LetsGetDangerous and similar qualities. Compare ItsPersonal. See also PretextForWar, when the trigger is a blown out of proportion to start the war.

You can expect that this declaration will be followed by a RoaringRampageOfRevenge and/or a NoHoldsBarredBeatdown.

Not to be confused with the 2012 romantic action-comedy film.
----
!!Examples

[[foldercontrol]]

[[folder:Anime & Manga]]
* ''Anime/ReadOrDie'': The leader of the I-jin has revealed himself, announced his ApocalypseHow and revealed [[spoiler:Nancy is Mata Hari and spying for them]]. In response, Gentleman informs Joker over the PA that Operation Manuscript Retrieval is suspended...
-->'''Joker:''' British Library Special Engineer Force, suspend Operation Manuscript Retrieval immediately. As of now, we begin "Operation Exterminate I-Jin Corps!" ''(cheers)''
* Also a CrowningMomentOfAwesome, Luffy and the crew (Mostly Sogeking) from ''OnePiece'' declare war on the World Government by not only shooting the Government Flag, but burning it as well. As it stands atop a major governmental base. Being watched by hundreds of marines.
** Later, Admiral Kizaru is fighting with four of the most powerful rookie pirates in the world. He's clearly toying with them, but doesn't go for the finishing blow. Then one of them hits him with a surprise attack that cuts him in half and blows the pieces to smithereens. After he pulls himself back together, he's clearly had enough. He then declares the fight is over and dispatches them all in a matter of seconds.
** Luffy has now declared war on [[spoiler: one of the Four Emperors, Big Mom.]]
* In {{Berserk}}, Guts gives a RousingSpeech variant of this against [[spoiler: The Apostles and The Godhand after surviving The Eclipse.]]
** Theresia declares war on Guts simply with a [[DeathGlare look]]. It's true that an [[http://view.thespectrum.net/series/berserk-volume-01.html?ch=Volume+03&page=165 actual declaration happens on the following page]], but [[http://view.thespectrum.net/series/berserk-volume-01.html?ch=Volume+03&page=164 the look]] conveys the message a lot better. And is also rather scary.
* Volume 3 of ''{{Hellsing}}'' has [[{{Ghostapo}} Millenium]] essentially declare war on Hellsing when they openly send one of their operatives, backed up by troops from the local law enforcement, to attack Alucard and Seras, live on national television no less. Just in case they didn't get the message, Volume 4 has them send a messanger to Hellsing headquarters with a live link to the Major, so that he can pretty much say "Let's fight!".
* The homunculi of ''Manga/FullmetalAlchemist'' caused major problems for themselves because of this trope. Before [[spoiler:Maes Hughes' death]], Mustang knew pretty much nothing about the homunculi and consequently was not involved in trying to stop their evil schemes. The moment one of them [[spoiler:killed Hughes]], he quietly went into a sort of chronic HeroicBSOD mode and became such a danger to them that Lust finally decided [[spoiler:he wasn't worth it as a sacrifice and simply tried to kill him]].
* In {{Naruto}}, Tobi declares war on the entire ninja world after the Kages refusal to hand over Naruto and Bee, starting the fourth great ninja war.
* In ''LightNovel/ACertainMagicalIndex'' Last Order steals Misaka-10032's goggles and taunts her before running off. 10032 [[DisproportionateRetribution loads her submachine gun with (thankfully) rubber bullets]] and declares it's time for a revolution.
* In ''Manga/JojosBizarreAdventure'' Part 2 (''Battle Tendency''), the vampire [[spoiler:Straizo]] claims to have killed Robert E.O. Speedwagon. Joseph Joestar, who viewed Speedwagon as an uncle, responds by pulling a Tommy gun out of HammerSpace, giving the blood-sucker several dozen new orifices, and then issuing a declaration of war. Appropriately enough, Joseph is a GuileHero who's occasionally been referred to as Japan's answer to WesternAnimation/BugsBunny.
** In ''VideoGame/JojosBizarreAdventureAllStarBattle'', Joseph has a super move which re-creates this scene; its name is, of course, the same as this trope's.
* ''Anime/CrossAnge'': After being publically humiliated, whipped, and nearly hanged in the hometown that once treasured her, and knowing that life as a Norma in Arzenal is a literally thankless dead end, Ange declares that she wants to destroy the entire world. Hilda, who was just rejected by her own mother, is only too happy to oblige.
[[/folder]]

[[folder:Comics]]
* Played for drama in the ''ComicBook/AstroCity'' story "Serpent's Teeth", when an alternate-timeline version of Jack-in-the-Box's son uses Jack's "Of course you realize, this means war" as motivation to become a KnightTemplar on the city's criminals... without realizing Jack was quoting BugsBunny.
* In ''ComicBook/TheSmurfs'' comic book story "The Smurf Threat", the Grey Smurfs send an {{Arrowgram}} to the Smurfs, warning them to surrender Hefty or else. Papa Smurf refuses to turn over Hefty to the Grey Smurfs, and the next {{Arrowgram}} reads something to the effect of "this means war" -- with the next thing the Smurfs see is the Grey Smurfs surrounding the village.
* In the second story-arc of ''ComicBook/MyLittlePonyFriendshipIsMagicIDW'' Rainbow Dash jokingly says this to Pinkie Pie at the slumber party when the latter initiates a pillow fight.
[[/folder]]

[[folder:Films -- Live-Action]]
* ''Film/DuckSoup'' and the MarxBrothers used this as a {{Catchphrase}} well before WesternAnimation/LooneyTunes did. They even made a song out of it.
** Groucho alludes back to it in ''ANightAtTheOpera''.
* In Creator/ChuckNorris movies, they'd abuse his woman, destroy his truck, and [[KickTheDog kick his dog]]... but when they [[BerserkButton messed with his hat]], "Oh, it's on."
* ''Film/{{Serenity}}'': "So no more running. I aim to misbehave."
* WrongIsRight: The US president uses this reason to invade the Middle East after 2 nuclear warheads are found in New York City. However, the film is a parody of PatrioticFervor and {{Eagleland}} as the warheads were allowed into the city to ensure the president's re-election.[[http://en.wikipedia.org/wiki/Wrong_Is_Right]][[http://www.youtube.com/watch?v=7IUbBdcDEo0]]
* The trope as used in the WesternAnimation/LooneyTunes cartoons is referenced in ''Film/WhoFramedRogerRabbit'': WesternAnimation/DaffyDuck says the exact phrase when DonaldDuck drops a piano lid on his head during their [[strike:duet]] duel.
* ''Film/JohnnyDangerously''
--> [[{{Malaproper}} Roman Moroni]]: "This is [[GoshDangItToHeck fargin]] war!"
* Layla, one of the characters in the superhero film [[SkyHigh Sky High]], won't use her powers except in self-defense, which means she gets relegated to the Sidekick track, constantly teased, and thought of as a complete wimp. Then one of the bad guys, convinced that their side is about to be victorious and not being able to resist, slaps her. [[spoiler:"Big. Mistake."]]
* ''Film/TheChargeOfTheLightBrigade'' has a doozy from Lord Raglan, describing the outbreak of the CrimeanWar. Intended InUniverse as a RousingSpeech to his staff, it plays as a paranoid rant:
-->"This means war, gentlemen! Our passage to India is threatened, I should think, wouldn't you? The honour, the reputation, the glory of England is threatened. Our [[UsefulNotes/QueenVictoria Queen's Majesty]] is sure to be threatened, she is... If the Turks go down like cards, flip-flop, then next up our own Solent, against our own Queen will come the Russians - ships and guns to rip our country into shame.
[[/folder]]

[[folder:Literature]]
* Used with a LampshadeHanging in ''Literature/AnansiBoys''.
* The novel ''Point of Impact'', made into a movie called ''Shooter'', had Bob Lee Swagger get upset when they [[spoiler:framed him for trying to kill the President and tried to kill him]]. But he really declared war when [[spoiler:they killed his dog]]!
* ''Literature/TheDresdenFiles''
** ''Literature/DeadBeat''. After finishing the job he was forced into by the [[OurVampiresAreDifferent Black Court Vampire]] Mavra when she blackmailed Murphy, Harry said this and threatened that if she ever went after Murphy or any other of his friends again he would take up every weapon he has to his potential and go after her and kill her. It has so far been taken seriously as she hasn't reappeared since. [[ChekovsGun Yet]]
** Fast forward to ''Literature/{{Changes}}'': [[spoiler: when his daughter, whom he didn't know about, was kidnapped by the Red Court, he showed that he hadn't been kidding with the above threat. He took up every weapon he had, including becoming the [[DealWithTheDevil Winter Knight]]. The only ones he didn't pick up was the [[PoweredByAForsakenChild Darkhollow]] and the [[FallenAngel Denarius]] and he would have if it would have been necessary.]] When the dust had settled [[spoiler:[[GuiltFreeExterminationWar the Red Court was no more]]]]
** Happens a couple other times too. [[spoiler: Molly getting dragged into Arctis Tor, the Nickelheads kidnapping Ivy, one side story when Michael's daughter is nearly killed, Bianca after Susan was turned...]] Let's face it. If you truly piss off Harry, stick you head between your knees and kiss your sorry ass goodbye.
** Also the {{Jerkass}} that dared to try and hit Mouse with a truck. [[AnAesop Moral of the story kids?]] Never mess with Harry's TrueCompanions.

* Though not in the literal sense, [[Literature/AnneofGreenGables Anne Shirley]], declares war on Gilbert Blythe after he teases her for her [[BerserkButton red hair]] by calling her "Carrots". She becomes his academic rival, and vows that she will always beat him and never forgive him. She eventually does forgive him, and goes one step further by [[spoiler: marrying him]].
* In the appendices to TheLordOfTheRings, the section Of The Dwarves recounts how Thorin's grandfather went to Moria and was caught by orcs, who threw out his head with a purse of small coins stuffed in the mouth. The purse was taken to the Dwarf-king Nain who regarded it in silence for a day or two, then said "This cannot be borne". The dwarves suffered horribly in the years that followed, but the orcs of the Misty Mountains took a ''hiding''.
* In Roman mythology an Etruscan RoyalBrat decided it would be a good idea to rape a respectable ''Roman'' woman named Lucreta. Naturally this meant war. [[MuggingTheMonster With Rome]]. As in the future [[BadassArmy most famous millitary power in civilization]].
* In ''[[Literature/HonorHarrington Mission of Honor]]'', [[spoiler:an entire treecat clan is wiped out during Oyster Bay. In ''A Rising Thunder'' it turns out that one member of the clan was visiting a neighboring clan and survived... and now the treecats have declared war on Mesa.]] For the uninitiated, a treecat is a telepathic, six-limbed, furry buzzsaw of ''DOOM''.
* ''Fattypuffs & Thinifers'':
-->At that moment a soldier entered bearing a message from President Rugifer. It said that the proposal which he had sent by his secretary was the last he would make, that it was an ultimatum, that he gave the Fattypuffs ten minutes to accept it and that he had ordered his train and would leave immediately if his wishes were not complied with.\\
"This means war!" said Marshal Puff in despair.\\
"''C'est la guerre!''" repeated Professor Ramfatty with satisfaction.
[[/folder]]

[[folder:Live-Action TV]]
* ''Series/DoctorWho'':
** The 10th Doctor in "The Idiot's Lantern".
--->'''The Doctor:''' The street. They left her in the street. They took her face, and just chucked her out and left her in the street. And as a result, that makes things... simple. Very very simple. Do you know why?\\
'''Inspector Bishop:''' No.\\
'''The Doctor:''' Because now, Detective Inspector Bishop, there is no power on this earth that can stop me!
** This a trait that [[BewareTheNiceOnes all Doctors]] can show pieces of. Although they rarely [[TechnicalPacifist use the word 'war']], if you hurt anyone close to them, ''anyone'' they love, you will '''pay'''.
** Played straight as an arrow in the appropriately-titled Series Six midseason cliffhanger "[[ExactlyWhatItSaysOnTheTin A Good Man Goes to War"]].
** The title doesn't just describe the Doctor, but also ''[[BewareTheNiceOnes Rory]]''. After the Silence kidnapped Amy and his unborn baby, Rory immediately goes on the war-path, even going so far as to storm through a Cyberman warship and scaring the crap out of them for information.
---> '''Rory''': '''[[PunctuatedForEmphasis Where! Is! My! WIFE?!]]'''
** Defied in the later episode, "Doomsday":
--->'''Cyberman:''' Daleks, be warned. You have declared war upon the Cybermen.\\
'''Dalek Sec:''' This is not war! [[ThisIsPestControl THIS IS PEST CONTROL!]]
* On ''Series/GoodEats'', host Alton Brown, in response to one of the Mad French Chef's declarations, said to the camera, "I hope he knows, this means war!" in a fake French accent.
** He also declares war on a cupcake shop that's run like a fancy restaurant, complete with a maitre'd taking reservations out front, saying that they're sucking all the joy out of cupcakes.
* Played with on ''Series/{{Supernatural}}'', when Dean tells Rufus, "It's war, you hear me? It's war!" The latter replies with, "You're damn right it is," before punching Dean in the face, not realizing that he actually meant ''[[HorsemenOfTheApocalypse War]]''.
* In ''GossipGirl''s fourth season Chuck declares war on Blair after she drives Eva away, though one might wonder where he feels entitled to declare war over something like that after he sold Blair for a hotel and slept with her nemesis in the previous season. Chuck and Blair are then at war for a few episodes until Nate and Serena sit them down and write an actual legally binding peace treaty. These kids sure do take things seriously...
* On ''BoyMeetsWorld'', Rachel actually says these words after she fails to get Cory and Shawn in trouble for a prank they pulled on her. This leads to an EscalatingWar.
* ''Series/BattlestarGalacticaReimagined''. This quote is often used in trailers, fan-made or otherwise.
-->''"This is the [[TheCaptain Commander]]. Moments ago, [[TheBattleStar this ship]] received word of a [[RobotWar Cylon attack]] against our homeworlds is under way. We do not know the size or the disposition or the strength of the enemy forces, but all indications point to a massive assault against Colonial defenses. Admiral Nagala has taken personal command of the Fleet aboard the [[CoolShip battlestar Atlantia]] following the complete destruction of Picon Fleet Headquarters in the first wave of the attacks. "How? Why?" doesn't really matter now. What does matter is that as of this moment, we are at war. You've trained for this. You're ready for this. [[LawfulGood Stand to your duties]], [[DysfunctionJunction trust your fellow shipmates]], and we'll all get through this. Further updates as we get them. Thank you."''
* In ''Series/{{Zoey 101}}'', Zoey tries to avoid retaliation by the girls during the guys' Prank Week. Until she gets soaked by an extra-large water balloon:
-->''Allright. This. Means. War.
* In ''Series/BabylonFive'', after breaking away from Earth due to the unconstitutional and tyrannical rule of [[PresidentEvil President William Morgan Clark,]] Babylon 5 essentially enters a cold war period with Earth that lasts through the second half of Season 3 and the first half of Season 4, until President Clark begins ordering ships to shoot on defenseless civilian and medical transports resulting in the murder of over 10,000 people. [[ThisIsUnforgivable Captain Sheridan immediately declares that this is the last straw,]] beginning the Earth Alliance Civil War.
-->'''Captain John Sheridan''': [[CaptainsLog Captain's personal log.]] September 2nd, 2261. ''Enough is enough!''
[[/folder]]

[[folder:Music]]
* HedPE's song "War" begins with this line.
* Ill Niño's song "This Is War".
* Attack Attack! (the US band) released an album in 2012 titled "This Means War."
* Petra's 1987 album and single, "This Means War!"
[[/folder]]

[[folder:Tabletop Games]]
* In {{Traveller}}, the titular Travellers make sure to not do ''anything'' that louses up the Imperium's internal economic and political cohesion. Small wars between sub-states are ok; after all boys will be boys. But if you extend your war too far and bother your neighbors, use [[WeaponOfMassDestruction Weapons of Mass Destruction]] or otherwise become too much of a trouble then you will receive a visit from the SpaceMarines.
* In ''TabletopGame/{{Shadowrun}}'', a Fatwa was issued in Teheran against metahumans and the Awakened. In response, the Great Dragon Aden went there and made the declaration "if you desire war, then see what you would make war against!" He then proceeded to destroy the city. [[PersonOfMassDestruction Personally]].
[[/folder]]

[[folder:Theatre]]
* In ''Theatre/OfTheeISing'', the French Ambassador is just declaring war on the United States on the grounds of President Wintergreen's refusal to marry Diana Deveraux, when Vice-President Throttlebottom invokes a [[TwentyFifthAmendment Constitutional article]] to assume the President's obligations and [[PairTheSpares marry her himself]].
[[/folder]]

[[folder:Video Games]]
* Subverted in ''Film/TheGodfather'' game. Shopkeepers and racket bosses will fight back if you apply too much pressure on them and you won't be able to get a payout from them... but since your pressure-application would probably have involved hitting them, shooting them, harming or killing innocents, all this does is mark them as TooDumbToLive. Sure, you'll need to come back in a week's in-game time to try again should you kill them, but really, they knew what would ensue...
* In the ''VideoGame/SamAndMaxFreelancePolice'' game ''Abe Lincoln Must Die!'', The Soda Poppers, a triplet of {{Former Child Star}}s, have become governors of Dakota. You are supposed to rile up their latent SiblingRivalry until:
-->'''Specs:''' Of course you realise. This means war!
-->'''Peepers:''' WAR!
-->'''Whizzer:''' WAR!
* In ''WorldOfWarcraft'', King Varian after the Wrathgate incident, and the subsequent Battle for the Undercity.
* ''[[{{Kirby}} "Hey, Kirby! This means war! If you can stack this many *'s, you win!"]]''
* PlayedForLaughs in the ''VideoGame/MassEffect3'' Citadel DLC: By this stage a lot has been done to Shepard, and the plot is someone is trying to kill her/him, [[spoiler: a Cerberus clone.]] S/he brushes off numerous insults, KickTheDog moments and attempts on her/his life until [[spoiler: the clone]] tries to dispose of Shepard's pet space hamster. S/he reacts the same as s/he does in regards to Batarian slavers, finding David Archer, and the renegade resolution to Tali's trial. Combined.
-->'''Shepard''': They messed with my hamster, guys. ''Now it's personal.''
* In ''VideoGame/DragonAgeII'', Meredith's decision to issue the right of annulment on the Kirkwall Circle, despite having nothing to do with [[spoiler: Anders' destruction of the Chantry]] causes the Mages in Kirkwall to finally have enough, with their rebellion either supported or quashed by Hawke. The events at Kirkwall later ripple across the face of Thedas and lead to other Circles rising up as a result, leading to the [[PretextForWar outbreak of open war]], three years later.
* In ''VideoGame/SaintsRowTheThird'', Monica Hughes almost says this (her exact words are "this is war") when Killbane has the Hughes bridge destroyed.
[[/folder]]

[[folder:Web Comics]]
* Yoda quotes the trope verbatim (and [[TheMarxBrothers Groucho Marx]] ''almost'' verbatim) in [[http://www.darthsanddroids.net/episodes/0611.html this]] episode of ''Webcomic/DarthsAndDroids''.
-->'''Yoda:''' You realise... this means war.
* ''Webcomic/SluggyFreelance'':
-->'''Messenger:''' My King, ''[this letter's]'' from Warlord Torgamous. It says "Your mustache smells like parmesan."\\
'''Sighard Lionson:''' '''[[http://sluggy.com/comics/archives/daily/990721 THIS MEANS WAR!]]'''
* Said verbatim by the Eddy the Wizard in ''Webcomic/YetAnotherFantasyGamerComic''. But then again, [[http://yafgc.net/?id=907 he has good reasons too.]]
* Chaos of Webcomic/LifeAndDeath ''almost'' does this, but doesn't due to a coin toss. But still, you have to wonder. [[BewareTheNiceOnes How indirect can he get?]]
* ''Webcomic/TheWhiteboard'': After digging out from beneath a whole bunch of snow dumped on her, Kasi informs Doc "[[http://www.the-whiteboard.com/autotwb1184.html You realize, of course...]] that this means '''War'''."
* After being turned into a [[GenderBender goth chick]] in one of the Newspaper arcs, Raven in ''Webcomic/ElGoonishShive'' responded [[NoFourthWall by threatening the author]] with "to quote a rabbit who was quoting Groucho Marx, of course you know this means war."
[[/folder]]

[[folder:Web Original]]
* At the climax of ''WebVideo/TheCartoonMan'', Simon pushes Roy a bit too far, causing him to say the line, "You do realize of course that ''this means war''!" and begin an over-the-top ''WesternAnimation/LooneyTunes''-style cartoon battle.
[[/folder]]

[[folder:Western Animation]]
* ''WesternAnimation/LooneyTunes'': A Characters/BugsBunny {{Catchphrase}} of course ("Of course you realise, dis means war!") -- any time Elmer Fudd, Yosemite Sam or some other [[strike:buffoon]] maroon harasses him to this point.
* Bugs Bunny's ''WesternAnimation/TinyToonAdventures'' counterpart Buster Bunny would say "It's time to party - Buster-style!" in the same kind of situation that would prompt Bugs declaring war on whoever's provoked his ire.
* The ''WesternAnimation/{{Animaniacs}}'' episode "King Yakko" has the bad guy say "this means war" when his first attempt to take over Anvilania fails. However, he was holding his hands over his head when he said it, leading to Yakko's rejoinder:
--> '''Yakko:''' "I thought that meant 'touchdown'."
** Slappy Squirrel (who is a clear expy of the likes of Screwy Squirrel, Bugs Bunny and the may other characters who embodied this trope in the golden age of animation) will make your life hell if you cross her, even if it's just for petty issues. Just ask the neighbor she drove to insanity because said neighbor wouldn't let her throw away a soda can in her trash.
--> '''Slappy:''' If I was a better person, I'd ignore this and move on with my life. But I'm not!
* In some [[ClassicDisneyShorts old Disney toons]], DonaldDuck would utter "That's the last straw!" before getting medieval on the ass of whoever dared to push his BerserkButton way too much.
* ''WesternAnimation/FamilyGuy'':
** In one episode, Lois gets splashed on by a car driven by her rival, who constantly beats her for the award for best piano student. Needless to say, This Means War.
** In another episode, a bomb blows up in Meg's face, which leads to her suddenly having a duck bill backwards on her head... exactly like what happens to WesternAnimation/DaffyDuck in ''WesternAnimation/LooneyTunes''. She then says, "Of course you realize, this means war!".
** Brian in "Halloween on Spooner Street", when he tried to reason with the bullies who took Stewie's candy, only for them to dye his fur pink.
* In ''WesternAnimation/{{DuckTales}}'', Fenton Crackshell (prior to his becoming Gizmoduck) declares to the Beagle Boys, "Of course you realize, this means . . . a skirmish."
* Tarantulas mutters it in an episode of ''WesternAnimation/BeastWars'', after Blackarachnia turns on him (again).
* During one of the "Spacecataz" segments, Oglethorpe and Emory have the following discussion after the Mooninites expose themselves at them:
-->'''Emory:''' Hey, maybe we should just back off. I mean, this is how fight starts.
-->'''Oglethorpe:''' This is not a fight... ''THIS IS A WAR!''
* {{Popeye}} in the face of abuse, he would finally roar, "I've had all that I can stands, and I can't stands no more!"
* Non-humorous example on ''WesternAnimation/{{Gargoyles}}''. When Xanatos [[spoiler: turns Derek into a mutate]], Elisa tells him that it's war now, and that she won't give up until she gets him back for it. It escalates to the point where [[spoiler: when Fox turns into a werefox]], Xanatos has to beg Elisa for help, and even then Goliath had to talk it over with her in private before she'd do it.
* In ''WesternAnimation/TheSmurfs'' episode "All's Smurfy That Ends Smurfy", the fairy Prince Garth declares war on the Smurfs for supposedly stealing their gold, which turns out to be the work of Gargamel.
* Used somewhat frequently in ''{{Spongebob Squarepants}}''
** The episode ''"The Battle of Bikini Bottom"'' revolves around SpongeBob and Patrick having a "war" over cleanliness and dirtiness.
** In ''"The Krusty Plate"'' Spongebob is instructed to wash a plate and the fallowing scene ensues.
-->[washes the plate but the spot is still on there]
-->'''SpongeBob:''' You're a tough little guy, aren't ya?
-->[tries to clean it some more but it's not coming off]
-->'''SpongeBob:''' '''{{This means war}}'''!
* In ''WesternAnimation/TheAdventuresOfSuperMarioBros3'', Kootie Pie, upset at being insulted by Bully, yells this before starting a garbage fight.
* Variations of this phrase (one of which is in the [[Quotes/ThisMeansWar Quotes section]]) are used in ''WesternAnimation/MyLittlePonyFriendshipIsMagic'', often PunctuatedForEmphasis.

[[/folder]]

[[folder:Real Life]]
* The immediate lead-up to and course of UsefulNotes/WorldWarI is famously complicated, but suffice it to say that this phrase got tossed around a whole lot right after Archduke Ferdinand was assassinated, as pretty much everyone wanted a war.
** Austria-Hungary (Central Powers) wanted to crush Serbia's military Junta and end their campaign of state-sponsored terrorism by replacing them with a stable and peaceful government.
** Russia (Entente) was unwilling to look bad on the international stage by refusing to support Serbia after so many perceived humiliations in recent decades, wanted to expand her influence in The Balkans, was sure she could defeat Austria-Hungary, and was confident France would help if Germany got involved.
** Germany (Central Powers) was deeply pessimistic about her chances in a war with France and Russia and hated to be dragged into a war over something as stupid as this, but was terrified of facing them alone.
** France (Entente) was supremely confident that her army was the best in Europe, wanted to conquer Alsace-Lorraine, cynically noted that now was the best time for a war[[note]] Germany and Austria-Hungary had only nominally participated in the general European arms-race of 1911-14 - right now the Entente had a decisive material and trained-manpower advantage, but given time the Central Powers might find the money to counter that with spending of their own [[/note]], and knew that this was her best chance to get Russia on her side in a war against Germany (since it involved Russian interests, whereas if it only involved French interests then Russia couldn't be counted on to join).
** Britain (Entente) was looking for a convenient 'out' to dangerous levels of popular unrest at home and jumped at the chance to grab German colonies and German ships and devastate Germany's economy. But the Cabinet was still divided over getting involved and the waverers staked their involvement a cause that opinion polls told them the British Public ''would'' back - guaranteeing Belgian Neutrality (and, indirectly, upholding the [[NapoleonicWars post-Great War]] European order that Britain had helped shape in 1815).
** Russia (Entente) wanted the end of the Ottoman Empire and chunks of Ottoman territory. [[FalseFlagOperation When Germany ordered the German crew of an Ottoman Navy ship to bombard Russian ports]], Russia refused the Ottomans' apology and declared war on them.
** [[NoMoreEmperors Yuan Shikai's China]] (Entente) wanted German Qingdao.
** ''Japan'' (Entente) wanted German Qingdao, and German Pacific Territories.
** Italy (Entente, 1915) wanted large chunks of Austro-Hungarian territory that the latter was not willing to give her.
** Bulgaria (Central Powers, 1915) wanted parts of Serbia and Rumania.
** Rumania (Entente, 1916) wanted parts of Hungary and Bulgaria.
** The USA (Entente, 1917) wanted a say in the post-war peace settlement without sacrificing too many of her own people.
* On October 28, 1940, the Italian Ambassador to Greece presented a three-hour ultimatum to Prime Minister Ioannis Metaxas, demanding that Italian troops be allowed free passage to unspecified strategic points throughout Greek territory. Today, Greeks acclaim Metaxas' reply via "Ohi Day," or "No! Day," but Metaxas' actual response was ''[[BilingualBonus "Alors, c'est la guerre!"]]'' [[note]]"Then, it is war."[[/note]]
* The picture above is the USS ''Arizona'' burning in [[UsefulNotes/WorldWarII Pearl Harbor]]. Japanese Naval Marshal General Isoroku Yamamoto is alleged to have said:
-->"I fear that all we have done is [[AwakeningTheSleepingGiant awakened a sleeping giant]], [[OhCrap and filled it with a desire for vengeance."]]
** Although he [[BeamMeUpScotty probably didn't say those exact words]], he did think that way... and he was right.
** President Roosevelt said something more true to the trope title: "Yesterday, December 7, 1941--a date which will live in infamy..." If this doesn't sound badass to you, remember what "infamy" means: what he essentially said was "ThisIsUnforgivable, and we shall never forget it." Less than one hour after those words were spoken, America officially declared war.
* Charles Francis Adams was the American ambassador to England during UsefulNotes/TheAmericanCivilWar. He was convinced that a British company was building warships for the Confederacy. He sent a series of notes to the British Foreign Minister insisting that the British government stop this, since England was supposed to be neutral. The last note contained the sentence: "It would be superfluous of me to point out to your Lordship that this is war." The British government bought the ships in question.
* While not a formal declaration of war, [[TheIrishQuestion when the government began executing the handful of captured rebel leaders of the Dublin Shoot-out/'Easter Rising']] on the grounds that they'd crossed a line by killing innocent people, well-known (Irish) 'Home Rule' supporter John Dillon rushed to London and warned Asquith (Prime Minister of the time) to halt the executions, saying: "You are washing our whole life work in a sea of blood." This was promptly ignored, and over time public opinion in the city and the rest of west-Britain came down on the side of the killers who ''hadn't'' been in uniform.
* Before the Six Day War, Israel specifically said that blocking the Straits of Tiran meant this. They weren't kidding.
* Likewise several maritime powers have a standing "This Means War" on anyone who captures Istanbul. The reason for this is that Constantinople keeps the Russian fleet [[SealedArmyInACan bottled up]] in the Black sea.
* The Latin phrase for this is ''Casus Belli'' and this is the version often used in diplo-speak. Actually it sounds scarier in English then in Latin despite the [[TheGloryThatWasRome reputation]] of the original Latin speakers.
* After the attack on Saguntum in the beginning of the Second Punic War the Roman ambassador to Carthage went before the Carthaginian Senate and said that he carried in the folds of his toga peace or war and demanded that they choose. The Carthaginians said "you choose". So the Roman said he let fall war. And the Carthaginians said, "We accept it".
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