Sometimes there are groups, nations, or entire species who protect their individuals fiercely. Though you might be dealing with anything from a Proud Warrior Race to a Hive Mind, be very careful how you treat its members, because they consider harm to one of them to be a declaration of war against all of them and will respond in kind.
An extreme form of Species Loyalty, this can be a product of Blue-and-Orange Morality, an Absolute Xenophobe or Paranoid mentality, or a convenient excuse made by a Blood Knight to declare war. Rationalizing the Overkill as a necessary duty to protect the whole is quite common and can lead to a Guilt-Free Extermination War. Such a group often applies Ape Shall Never Kill Ape to themselves and consider their code of conduct as The Right of a Superior Species, and will have no qualms about harming the individuals of their neighbors, often due to Moral Myopia, a Lack of Empathy for outsiders, or confidence in their superior strength.
While this seems like a villainous trope, heroic variants do pop up when a villain attacks one of the True Companions or (if someone has severe Chronic Hero Syndrome) an innocent bystander. This might absolutely confuse the villains, who can't figure out why someone they never messed with wants to attack them.
- Fairy Tail: The Fairy Tail Guild itself. Hurting any of their members is the same as declaring war. The best example is the Phantom Lord arc. The Phantoms trash their guild hall? They turn the other cheek. Attack some of their weaker members and crucify them on a tree? Nice knowing ya. And when it turns out they were actually hired to kidnap Lucy, they make sure that no one can get near her, despite the threat of annihilation.
- One Piece:
- Whitebeard is such a Papa Wolf to his subordinates that he's willing to go to an all-out war if one of them gets in danger. This is pretty much what started the Marineford arc.
- Arlong is like this. If any human attacks one of his henchmen, it'll mean bringing down the wrath of the entire Arlong Pirates- if you're lucky, they'll only kill you. If you're unlucky, they'll wipe out your entire town and god knows how many of your neighbors as an 'example' to the other towns they control.
- Hunter × Hunter: The people of Meteor City live by the adage "We will accept anything you give us, but please don't take anything away from us." They are extreme about that, as society at large found out the hard way when a Meteor City resident was arrested and sent to prison, which the people of Meteor City treated as a declaration of war. The incident prompted a large number of suicide bombers to simultaneously kill the entire court staff, all of the jury members, and all of the attorneys involved in the case. That being said, this was most likely orchestrated by Meteor City's head elder, who has the superpower to turn any surface or object explosive, including people, without them realizing it. That power has since been stolen by someone else.
- So I'm a Spider, So What? has Anogratch, a monkey like monster. Killing one will cause every single anogratch in large radius to target whoever killed the original one, and killing those causes more to get enraged. They are downright suicidal in their pursuit, to point of actively sacrificing themselves to give their brethren chance to kill the offender. Demon army successfully takes down a human fort by sneaking in one and letting humans killing it, causing a massive herd of anogratch to overrun the fort. Downside is that now not even demons can take the fort from its new residents.
- One of the reasons you really don't want to screw with some superhero teams. In Teen Titans, this trope got Invoked hard. Dr. Light made the fatal error of trying to hurt the new recruits and Dick Grayson got wind of it. Less than three phone calls later, he has damn near every surviving past and present Titan showing up to get a hit in on Light.
- Against The Moon: Sirius and James' actions fit this mindset, such as when they made Slytherin quills explode in retaliation for Slytherins vandalizing the book Remus checked out of the library in order to humiliate him.
Sirius: Because what? Got a guilty conscience, do you? Want to tell your Head of House what you think you did to deserve this?
- With this Ring... (Green Lantern): When Remoni-Notra challenges Star Sapphire to a duel, Hal Jordan warns her if she attacks Carol she'll be fighting the whole Green Lantern Corps.
Hal Jordan: "I warn you, lady, a move made on this woman will be considered a move against all of us."
- Crimson Tide: Rebel leader Radchenko tells the world that as president, he will kill ten thousand citizens of any nation who kills one Russian citizen.
- The Three Musketeers (1993): Girard ends up being chased by the entire musketeer force at the end of the film when he threatens D'Artagnan; After all, their motto starts with "All for one."
- Thor: After the frost giant attack on Asgard's treasure room that was easily repelled by the Destroyer, Thor calls it a declaration of War against Asgard while Odin dismisses it as the rash actions of a few individuals who paid for it with their lives.
- Watchmen: Rorschach says that the murder of the Comedian is an attack on all costumed vigilantes, retired or otherwise.
- In Spider-Man, the Green Goblin tries to force Spidey into making a Sadistic Choice - save his Love Interest, or a bunch of school children? What Goblin doesn't expect is for all the people on the bridge to try to help Spidey by pelting him with various objects. Over the din, two men's voice can be heard shouting:
Bystander 1: You mess with Spidey, you mess with New York!
Bystander 2: You mess with one of us, you mess with all of us!
- The Neverending Story: Seen with Gaya, the dark princess of Spook City and the Land of Ghosts. She turns on G'mork when he arrives searching for Atreyu, because he lets slip his true mission to bring about Fantastica's destruction. While it's implied Gaya is an evil or at least foul Fantastican, she nevertheless defends her world against G'mork.
"G'mork. You forgot that I too am one of the creatures of Fantastica. And that to fight against Fantastica is to fight against me. That makes you my enemy, and I've outsmarted you."
- Judge Dee uses a loophole that works like this: attacking an Imperial judge (in this case, trapping him under a giant bell to suffocate) is attacking the Imperial system, and therefore a crime against the state, allowing him to sentence a criminal before he can use his money and connections to get his case transferred. He even says it's following the letter rather than the spirit of the law, but it works.
- In A Brother's Price, this is the Whistler sisters' response to a threat to their sisters-in-law, the princesses. As Eldest says, "We Whistlers have an unbreakable rule you mess with one of us, you mess with us all!" This is said while at least a dozen rifles, in the hands of experts, are being aimed at the offenders.
- In the Gentleman Bastard, series, the Bondsmagi are Super Supremacists who have a simple rule for dealing with non-mages: they do whatever they want, and any harm to a Bondsmage is answered with ruthless Disproportionate Retribution.
- Babylon 5:
- The pilot episode The Gathering involves a plot to assassinate the Vorlon ambassador Kosh that nearly succeeds. While Kosh is being treated, the Vorlon empire sends a fleet of ships which are prepared to destroy the entire station and start a war if the accused commander Sinclair isn't handed over to them.
- In the prequel In The Beginning, the disastrous first contact event that results in a Human attack on a Minbari fleet which kills their leader Dukhat is taken as an assault on the entire Minbari race, and they embark on a genocidal holy war of revenge.
- In CSI: NY "Heroes," Mac says it right out. "You attack one, you attack us all." He initially meant the Marines as his case was that of a dead Marine, but it took on a double meaning when their former colleague Aiden was found as the episode's second victim.
- Chicago P.D.: It's demonstrated several times that attacking or hurting anyone on the Intelligence Unit or anyone they're close to is extremely ill-advised.
Burgess: "Thank you for taking this (her sister's rape) on."Voight: "An attack on your family is an attack on our family."
- Doctor Who: In the episode Cold War, the Doctor remarks that this is the Martian warrior code and the Ice Warrior general Skaldak later echoes the same. Skaldak sees his capture and imprisonment on the Russian submarine as an attack on the entire Ice Warrior race, and so intends to annihilate humanity as retribution.
- Firefly: This is the attitude the crew generally has toward each other. When Jayne tries to hand over Simon and River to the Alliance for monetary reward, Mal comes within a hairsbreadth of killing him for it (only Jayne expressing some genuine regret over his actions stops Mal). Later, the entire crew (including the noncombatants) take up arms in order to rescue Mal from Niska.
Jayne: What are you takin' it so personal for? It ain't like I ratted you out to the Feds.
Mal: Oh, but you did, Jayne. You turn on ANY of my crew, you turn on ME. But since that's a concept you can't seem to wrap your head around, then you got no place here. You did it to me, Jayne, and that's a fact.
- The Changelings, leaders of the Dominion in Star Trek: Deep Space Nine share experiences through the Great Link so anything that happens to one is literally experienced by all. This is implied to be the reason why they wanted to pacify the Alpha quadrant under the banner of the Dominion in the first place; their lost changeling Odo lived in the Alpha quadrant and refused to rejoin them, so they decided to make the Alpha quadrant part of their own territory in order to bring his "home" to him instead of the other way around.
- In the background material for Warhammer 40,000, the Kabals of the Drukhari are said to offer their treacherous and power-hungry members a measure of protection against external foes. The death of a Kabalite at the hands of an outsider is considered a hostile action against the Kabal as a whole and will result in immediate and violent retribution.
- Subverted in Warhammer Fantasy, where Brettonian nobles who go full Feudal Overlord (including Droit du Seigneur) can look forward to being besieged by a coalition of their neighbors. Not for the peasants' sake, of course, dirty, filthy little mongrels, but because such a thing reflects badly on all Brettonian nobs.
- Higurashi: When They Cry: The people of Hinamizawa have cultivated this kind of mindset amongst themselves. Keiichi witnesses this firsthand when he gets attacked by a group of delinquents in a neighboring town, and a couple dozen Hinamizawa residents (from schoolkids to the elderly) form up around them and look like they're about to get violent before the police break it up. Keiichi, although deeply grateful, remarks on how frightening the whole thing was, even though the villagers were ganging up on his behalf.
Hinamizawa Saying: If one person attacks you, fight back with two. If two attack you, fight back with four. And should a thousand people move against you, the whole village shall fight back as one.
- A heroic example in the Fantastic Four: World's Greatest Heroes episode "Doomsday"; when Dr. Doom attacks Reed, the other three attack him.
Ben: If you attack one of us, Doom... you attack all of us.
- In the pilot episode of Men in Black, agent J accidentally kills a Skraaldian in a sewer. The Skraaldian race have a Hive Mind and so their entire race marks J for death and tries to kill him in retribution. J only gets off when (a friend pretending to be) K show them a tissue he just blew his nose with, which is considered such a great insult that they forgot about J.
- The Avengers: Earth's Mightiest Heroes!: The entire Kree empire feels this way about any upstart race that would dare to resist them when they come to conquer. The first encounter with the Kree is just with one of their sentry robots which the Avengers have a tough time destroying. They meet a Kree officer who's much kinder and friendlier than his brethren, who tells them they've doomed themselves because just destroying the probe will bring the full weight of the Kree empire to Earth. Future encounters with the Kree show them to be just as arrogant and self-entitled as they're described. Their entire race takes it as a personal slight when the Avengers beat their champion and send them packing in their first proper invasion attempt.
- In Japan's Tokugawa Shogunate, any lord who attacked another lord was considered to be attacking the country as a whole, and could expect retribution from the shogun and his followers.
- Article 5 of the NATO charter explicitly states this. It was originally envisaged to discourage the Soviet Union from getting too expansionist in Europe, as any attack on a NATO country would draw every other member into the war — most notably, the United States and its nuclear arsenal. Thankfully, it never was invoked against the Soviet Union; the only time NATO has ever invoked Article 5 was after the September 11 attacks in the United States.
- These good intentions were strained twice in The '70s, when NATO was forced to ask what would happen if two of is member states were dragged into a shooting war... with each other. Iceland and Britain exchanged shots in a disagreement over fishing rights. Then, more seriously, Greece and Turkey ended up on the brink of all-out war over Cyprus. As a politician pointed out at the time, it makes the all-for-one principle a little bit less clear cut, as well as bloody embarrassing.note
- A lot of animals are known to do this. Bees, hornets, and wasps are the best known example where killing one releases pheromones that make the others more aggressive who now attack with much more intensity. Some species of birds are known to do this too, where an attack on one will mark the attacker as a threat, prompting all the others to attack it as a flock.