In Shakugan no Shana, the Flame Hazes tend to be lone wolf types and apparently it's unusual for Flame Hazes to ever work together, even though they have the same goals; Margery Daw is hostile when first encountered (she wanted to kill the one particular Tomogara who isn't harmful). Later, when Wilhelmina shows up, she conflicts with Shana, who has decided to save the world without killing Yuji.
Neon Genesis Evangelion, NERV is fighting to save the world the world from complete destruction, yet the UN keeps cutting its defence budget, heck it even wanted to Nuke Tokyo 3 into oblivion if the situation looks bleak. Might even be deliberate, seeing as after the Angels are destroyed, civil war swiftly erupts.
Somewhat justified in the fact that over the course of the series, Tokoyo-3 and the evas take an ernomous amount of damage, and NERV's infastructure is incredibly expensive just to begin with (Massive rifles for the Evas to use? Experimental particle beam weapons? That crap's not cheap). It's also implied that the economy of the post-2nd impact world is much worse then ours, particularly if doing your laundry and buying steak dinners is "expensive".
Cruel irony. The real reason NERV exists "is" to bring the End of the World itself on SEELE's terms. The only reason there was Civil War was because of Gendo Ikari attempting to hijack the End of the World himself.
In Code Geass, Lelouch and Suzaku want to make the world better. They also happen to be best friends. Unfortunately, Lelouch's best plans are too often foiled by Suzaku at the worst possible time, and Suzaku by himself is being used as a pawn by Britannia. Eventually Lelouch is expelled from the Black Knights due to a brutally effective ploy by Schneizel. Suzaku realizes what a jerkass he is being and that his plan simply won't work. Nuking a city and killing 30 million people on accident will do that to you, apparently. He finally decides to team up with the now isolated Lelouch.
Also, the Black Knights leaving the JLF to die. Nightmare of Nunnally takes this one step further into Zero and Kyoto flatly selling them out. They were too unpredictable.
At least twice in Dragon Ball Z, Vegeta would deliberately allow the Universe-Destroying Abomination Of The Week to power up so he could have a "worthy" opponent to fight —even going as far as to battle his own allies to let it happen. First, he did it in the Cell Saga, where he stood back while Cell attained his "Perfect" body, then battled Trunks, his own son, when the latter tried to stop it. In a later arc, when he and the other Z fighters raced to avoid the awakening of Majin Buu, he let the magician Babi Di empower him with a malevolent sigil, and forced Goku to battle him instead of helping save the world. Gohan and the Kaio-Shin were left to try to stop Buu on their own. Naturally, they failed, since Buu absorbed the Battle Aura shed by Vegeta and Goku in their duel.
Averted in Death Note: while Mello and Near start out as enemies (at least, from Mello's perspective), and when Mello visits the SPK headquarters he uses a hostage and is held at gunpoint, but instead gives him a vital- if cryptic- piece of information about Kira.
Cosmo Entelechia and Ala Alba are both trying to save the magic world in Mahou Sensei Negima!. The problem is that the former doesn't believe in the latter's plan, which has a more optimistic solution. Which is honestly justified considering the situation and who is informing them of it.
By volume 4 of Maiden Rose, Eurote and some aristocrats from Taki's country are so determined to get rid of Taki because he's second-in-line to the throne that their in-fighting becomes a great asset to the Western Alliance who they are currently at war with.
Narrowly averted in Naruto at the beginning of the Fourth Shinobi War. The Kages barely agree to forming an Alliance to counter Obito and their shinobi nearly start fighting one another over old grudges when assembling for battle against a common foe.
Extremely common in superhero comics, as many writers look for any excuse to have heroes fight each other. As a specific example, the official superteams of countries America is less than friendly with, like Marvels (former) Soviet Super Soldiers/Supreme Soviets/People's Protectorate/Winter Guard and DC's Big Ten (China's national super team) are always - ALWAYS - more interested in keeping American hero teams out of their home countries than they are in teaming up to stop the rampaging monster/villain/aliens/whatever that the American heroes have chased across their border.
That said, the People's Protectorate and the Avengers make for a pretty good team when they stop squabbling.
High Noon. Kane's deputy refuses to help him unless Kane agrees to the deputy becoming his successor.
In 1776, as well as in real life, Benjamin Franklin says "If we do not hang together, we shall most assuredly hang separately!" Also, until Richard Henry Lee brings Virginia's approval to debate the idea of independence, most of the congressmen refuse to second John Adams' proposal to debate independence. John Dickinson never stops supporting the crown however, even after his cause is lost, although that is not out of pure animosity towards Adams.
This trope plagues The Avengers for the first 2/3rds of the film, with their multi-sided bickering, mistrust, derision, and lack of professionalism leading them to be so wrapped up in yelling at each other that they fail to realize that Loki is actually counting on them to be so wrapped up in yelling at each other that they fail to head off an ambush, are swiftly laid siege to, the Helicarrier is badly crippled, their ranks are scattered, Loki escapes, and Coulson is killed. It's only after this happens that they retroactively realize they could've avoided it all if they had just worked together from the start.
Every film of George A. Romero's Living Dead series —save perhaps Dawn of the Dead— revolves almost entirely around this. No matter how petty the squabble or how many restless undead are pounding on the weakening barricades outside, the main characters will never, ever just swallow their pride and work together, because Romero is a strong believer in Humans Are the Real Monsters and he will get his pet message across even if he has to roll it up and cram it right down your throat.
In David Wingrove's Chung Kuo series: the Ping Tiao rebels, the Yu rebels, the businessmen in Europe and later the businessmen in North America, and of course Howard deVore's operations
In Ghostmaker, they have another rivalry between the Ghosts and the Volpone Bluebloods. While the Bluebloods themselves are not all evil, their commanders once wittingly bombarded where they knew the Ghosts were, and at the climax, two officers are in a brawl until a Chaos beast actually erupts on them, killing several of their troopers.
In Traitor General, Sturm blamed his fall on Gaunt's unwillingness to let the past go and jockeying for power. He realizes the truth, in time.
And of course there's Rawne, Gaunt's own third-in command, who has tried to kill Gaunt himself on several occasions. Admittedly this was because he blamed Gaunt for saving his regiment and not allowing them to fight the forces of Chaos at their Founding - even though doing so would have done no practical good at all, and would have rendered the Tanith people extinct.
In his Inquisitor series — both Eisenhorn and Ravenor — the inquisitors in question spend as much time resisting the Inquisition as they do the forces of Chaos.
In Brothers of the Snake, a Space Marine Khiron shot and killed another after a fight with Chaos forces. When another Marine, Priad, finds it hard to believe that he just murdered him and investigates, the squad of the dead Marine corner Priad in an attempt to intimidate him out of dishonoring them. Khiron had shot him because a daemon had possessed him, and Priad deduced that the captain of the squad was now possessed and killed him — fortunately, with evidence of the daemon.
In Titanicus, a member of Adeptus Mechanicus reveals a purported proof that the Omnissiah and the Emperor are not one and the same. This results in rupture with the order and with the Imperial forces — while the planet is being invaded. Fortunately, Varco's Heroic Sacrifice revealed more invaders, so they went to fight them instead. One conspirator, lamenting that Fire Forged Friendship would prevent support, reveals that the evidence had been tampered with, as part of a power ploy. Afterward, they do notice that "this was a power ploy" does not exactly exclude "this was true." They decide to black it out anyway, because even if true, the ensuing schism would be fatal to both sides.
In the Horus Heresy novel Legion, Namatjira learns that the Alpha Legion is operating on a planet he is trying to bring into compliance. When his subordinates speak of a lack of respect, Namatjira complains that it makes strategy impossible, because he does not know what his forces will be doing.
Cain also exploits this trope in the same novel by following a rival band of Chaos Space Marines into the facility and allowing them to do most of the work of clearing the defenses between him and the summoning, all the while trying not to provoke them himself.
In the Codex Alera series, as the extremely deadly Vord Queen and its millions of minions, execute many Curb-Stomp Battles on the Alerans, the First Lord realizes this trope will be true unless the Alerans forge alliances with all of their long-time enemies.
The Honor Harrington series had one of these on the Haven side - in War of Honor, one character (the Havenite Secretary of State) is sabotaging diplomatic communications to engineer a crisis that he can ride to the Presidency. His predictions of how everyone will react to the altered communications, particularly the person he wants to replace, are proven drastically wrong.
In Terry Pratchett's Discworld novel Night Watch Ned Coates fits this trope, at least in the scene where he tries to convince the members of the Watch not to follow Vimes, warning them that they'll all be killed. The kicker is that, since Vimes is from the future, he knows that Ned is almost certainly correct (he can't be 100% sure, because of quantum).
Wolfblade opens with Ragnar being sent to Terra to protect him from those who blame him for the loss of the Spear of Russ, who are partly motivated by rivalry within the Chapter. And on Terra, he finds himself in the thick of the rivalry of Navigator Houses.
In Lee Lightner's Sons of Fenris, Ragnar recognizes Dark Angels and reflects on their Chapters' long hostility. The Dark Angels and Space Wolves fight. When Ragnar and some others capture some Dark Angels, they both see the Commander attack and kill Dark Angels and Space Wolves. Jeremiah, the Dark Angel leader, gives his word that they will not try to escape, and Ragnar gives back their weapons — but the fighting still goes on about them while they take out the real foe. Later, Abandoned By The Cavalry occurs but was actually a feint; the Dark Angels could not tell the Space Wolves that, though, because they had only open comm channels.
In The Killing Ground, Uriel is enraged at the prospect of dying at the hands of a man whom they should fight beside and roars at him to kill him and be done. Whereupon Leodegarius explains that the third ordeal was that they lose to him. If they had defeated him, they would have proven they were tainted, but now they have been acquitted.
Conversely, on the Imperial side, the Space Marine captain sees great bitterness and division in a briefing meeting (partly fueled by a grievous failure on the part of some forces), and demonstrates with the sticks that can't be broken the danger of this. He cites their slogans and how they obviously pertain, and the quarreling factions reconcile.
In James Swallow's The Flight of the Eisenstein, Decius quarrels with Garro while forces loyal to Horus are actually attacking. Later, Voyen complains that his actions were foolish. When he suggests a Mercy Kill for a wounded Marine, Garro accuses him of wanting to suppress the evidence of what the lodge he belonged to did.
In Mike Lee's Fallen Angels, when they have found Chaos, the anger as they quarrel over how to deal with it and who is to blame is so plapable that Zahariel interposes himself between two Dark Angels. Later, Zahariel finds that the rebel forces are also quarreling among themselves.
In Black Tide, Noxx quarrels with Rafen about who should be in command.
In A Song of Ice and Fire, a civil war engulfs the seven kingdoms while a supernatural army is about to invade.
Even within the civil war there are elements of this. Robb Stark, Stannis and Renly all hate the Lannisters, but instead of teaming up against them Renly and Stannis fight each other and Robb refuses to set aside his crowd for an alliance with one of the Baratheon brothers.
The Lannisters all hate each other more than their enemies. Tywin particularly hate Tyrion and Cersei, and the two hate Tywin and each other all the same. When it seems they have won the war, they proceed focus their anger toward each other, in the end Tyrion kills Tywin and leaves Westeros, leaving Cersei as the one running things in Kings Lannding, things start going down hill fast for her and the rest of the house.
Changes hints that at least some of the bickering is fabricated to cover for the real plans.
In Nick Kyme's novel for Warhammer 40,000Salamander, although the Marines Malevolent have played The Cavalry, and they and the Salamanders are still on enemy territory, tension and sniping arise almost immediately on their meeting.
The Marines Malevolent are colossal Jerkass loose cannons even by Warhammer 40,000 standards, and almost everything they do results in this. Nobody likes them, especially not the Salamanders, who are as close to "nice" as Space Marines get.
Tsu'gan, dissatified with the new captain, foments discord in the company.
In this case, the difficulty can be traced to the rivalry that Fudge believes exists between him and Dumbledore. Having successfully defeated Grindelwald and opposed Voldemort before, were the Dark Lord to return again then Dumbledore would be the one people followed. With prompting from Lucius, Fudge happily buried his head in the sand.
In Norman Juster's The Phantom Tollbooth, the two kings know that bringing back the princesses Rhyme and Reason is what is really needed, but they'd rather disagree with each other. Until Milo points out that they are in agreement: they agree to disagree.
In David Brin's Startide Rising, the fleets of aliens hunting them does not prevent fierce infighting among the dolphin crew. (Fortunately, the aliens don't get along with each other, either.)
In The King Must Die, a bull-jumper is killed because his team does not help him, which would create some risk for them. Theseus points out to his team-mates how defeated the survivors look, and how certain they are to die, before having them take again The Promise that they will consider each other's lives as valuable as their own. Keeping it lets them outlive the rest, and indeed, other teams take the same oath and start to live longer, in imitation.
A chronic problem in the Codex Alera, to the point where the Alerans are so busy fighting amongst themselves that threats like the army of 60,000 Canim that landed on the coast or the Vord colonies that have already covered a continent and a half wind up taking a back seat in many people's minds (especiallythe Senators) to personal feuds and scrabbling for power. This gets to the point where, in the last book, Senator Valerian is trying to accuse Bernard of treason for fortifying the Calderon Valley (even though it's the only place left where they have any hope of holding back the Vord) and saying Doroga is an untrustworthy savage. So Lord Placida picks him up and throws him bodily out of the meeting.
The Wheel of Time is filled with those : Elaida, the Whitecloaks ( up to the point where Galad takes over, at least), the Seanchan, Andoran Houses contesting Elayne's claim to the throne, the Shaido, Carhienin and Tairen rebels...
Variants of this are all over Battle Royale, and in the novel this turns out to be the whole point of making the students kill each other. Every six months, everyone in Japan gets to see a broadcast giving the body count of a particular runthrough, categorized by means of death. They all have it ingrained in their minds that the people they grew up with are willing to kill them to survive. If they can't trust each other, they can't coordinate effectively to overthrow the government.
This trope is brought up in Star Trek: Destiny, though it's ultimately averted in one instance. As the Klingon Empire faces a massive Borg invasion, Martok's nemesis Councillor Kopek agrees this is no time for politics. When Martok, leading the Klingon fleet, calls Kopek back on Qo'noS to warn him of impending Borg attack, Kopek assures Martok his throne will be waiting for him upon his return. Martok replies "with you sitting in it, I imagine?" However, Kopek for once isn't planning anything, and says so. It's the first time the character has been presented as anything other than selfish; he understands the severity of the situation. He also dies defending Qo'noS, so possibly Redemption Equals Death.
In Aaron Allston's Galatea in 2-D, Donna and Roger quarrel bitterly, insulting each other, while in hiding in the hotel. Donna stalks off.
In Shanna Swendson's Once Upon Stilettos, they discover someone was at Owen's desk and hunt for The Mole. It may even be an operation to get them all Hanging Separately, they realize.
A massive problem for the good guys in the New Jedi Order series. Initially, the agents of the invading Yuuzhan Vong drove wedges into the New Republic themselves, dividing senators against each other, military leaders against politicians, and everybody against the Jedi. It only got worse when the galactic capital fell, as individual senators, planetary governments, and fleet commanders were left on their own initiative as the Republic tried to get back on its feet. Reorganizing the government into the Galactic Alliance and beefing up the federal government in general and the chief executive in particular helped smooth over the ideological differences, but damaged infrastructure would continue playing havoc with their efforts until the end of the war. (At one point, Chief of State Cal Omas claimed he had eight separate spy networks, none of which were in communication with each other... and he couldn't be certain there weren't others out there that didn't talk to him.)
Spike drove a wedge between the Scoobies in season 4 of Buffy. His plan was fatally flawed, but it made for a hell of a falling out between the gang, if only a temporary one.
This happens frequently in 24, usually in the form of an Obstructive Bureaucrat who doesn't understand that Jack Bauer is always right. Jack is often arrested or otherwise delayed by a new CTU director who generally gets in the way for the first few episodes after his introduction.
Maybourne and the NID do this a little in the first few seasons of Stargate SG-1. Particularly the episode "Politics," in which Daniel knows that the Goa'uld will attack Earth, and no one outside of the main characters believes him.
In the later season episode "Ethon", both the Rand Protectorate and their political and military rival, Calledonia, would rather nuke each other into the stone age than unite to oppose the impending Ori invasion. Even when a peaceful solution to their rivalry is offered, they still launched nuclear missiles against each other...
From Torchwood: Children of Earth. Say you're the British government. Say you have an alien problem. You also happen to know of an organisation which fights hostile aliens. It is willing to work with you. What are you going to do? That's right, put a bomb inside their leader's stomach.
On LOST, Jack Shepherd's statement that "Either we live together or we die alone" qualifies. Subverted in the Fourth Season Finale when Jack started to say it, only to have Rose interrupt to notify him that if he did so, she would punch him in the face.
New Jersey officers are portrayed as competing with New York ones for the chance to get the 'collar' (arresting a suspect). In one episode, a DA even remarks that New Jersey has an 'inferiority complex' about the NYPD getting in their affairs.
Police departments in parts of New York north of New York City ('upstate') and east of it (Long Island) as being at the best laid-back local sheriffs who don't like city-slicker interference and at worst in on the crime.
At various times, the Brooklyn and Bronx DA's are portrayed as headline-seeking opportunists more interested in padding conviction rates than actually ensuring the guilty are convicted.
Virtually all crime dramas portraying city-level police portray Federal authorities as authority wielding Men in Black who are all too willing to let a horrific crime go unpunished to further what they see as a bigger picture.
The only reason that the virus reaches the inside of the Big Brother house is because the housemates refused to believe Kelly. They soon changed their minds.
Grayson refuses to kill an infected Angel. He regrets it.
Patrick and Jonty open the gates holding the undead out in an escape bid, against the wishes of the rest of the group. The result? Everybody dies.
Warhammer 40,000 takes this to insane levels (look at how many Literature examples it has!). 'There is no innocence, only shades of guilt.' Everyone is held in the darkest suspicion of heretical thought, Entire worlds are lost while organizations bicker over their jurisdiction. The only person above reproach is named the The Immortal God Emperor of Mankind and he might be dead.
The Imperium has at least half a dozen Thoughts For The Day dedicated to this, among them "Divided we stand, united we fall". Considering the extreme hierarchical nature of the Imperium, a few higher-ups going rogue could (and has) lead to massive problems - Some regiments probably only recognized their superiors turning to the side of Chaos a few weeks after being told to paint those cool stars over their old insignia.
The present Imperial is extremely decentralised, though, after the Thorian Reformation no one power group has control over the Imperium, and there are several extremely powerful watchdog organizations in place to control abuses of power. And burn heretics, of course.
This state of affairs came about as a direct result of the Age of Apostasy, where due to some complex political maneuvering one man, Goge Vandire, became head of the Administratum, the Ecclesiarchy, the Imperial Assassins, and (as a result of controlling the entire supply chain and being able to excommunicate anyone he wanted) de facto leader of both the Imperial Guard and the Imperial Navy. He promptly set himself up as Emperor-in-all-but-name, established a rule that became notably for its tyranny, despotism, and body count even by Warhammer standards, acquired a harem/bodyguard of elite fanatics, and had a personal fleet of warrior-priests who went around purging everyone who might be a threat. Only the Space Marines and (parts of) the Adeptus Mechanicus remained outside of his command, mostly because they withdrew into their own fiefdoms. Needless to say, nobody is eager to let it happen again, hence the decentralized command structure.
Said organisations are also hanging separately. The Inquisition spends hours in philosophical debate with a bolter in one hand and a power sword in the other. Oh dear.
You have this problem within organizations within the Imperium, with many sub-factions constantly fighting each other, sometime literal. One common justification for Imperium players to fight each other on the tabletop is that both companies got the same order to get some holy item and bring it to their superiors, fighting to the death to just make sure the other guy doesn't do it first. On a grander scale, you would think the Tau, Eldar, and Imperium would work together more often against the Cyborg skeletons, raving green brutes, galaxy eating bugs, and the literal legions of Hell
Exalted, oh so very much. Solars, Lunars, Sidereals and Dragon-Blooded are all trying to protect Creation in their own way; it's just that the Dragon-Blooded's way involves demonizing all the others to keep their orderly society going, the Sidereals' way involves manipulating said society from behind the scenes because they don't trust any of the others with power, and the Lunars' way involves tearing down said society because of its increasing corruption and instability. The end result is Creation's heroes spending a whole lot of effort fighting each other when they could be fighting the Abyssals, Deathlords, Fair Folk, and other forces who want to destroy the world.
Hunter: The Vigil has its own version, as a good number of the Compacts and Conspiracies are at direct odds with one another. Let's see, Task Force VALKYRIE wants to deal with the supernatural in secret, while Network Zero wants to blow open the Masquerade through new media. The Long Night are premillenialist Christians aimed at "redeeming" monsters who view the Malleus Malificarum, the Catholic Church's black bag group, as followers of "the Great Whore of Babylon." The Philadelphia sample setting takes it a few degrees further, with the general mood of "Not In My Backyard" and an emphasis on how the hunters are more devoted to territorial pissing than, you know, monster hunting.
In BattleTech, the Free Worlds League is subject to a lot of infighting. And then, after the Jihad, it literally fell apart.
During the Clan Invasion, the invading Clans all have personal grudges against each other, most notably the Jade Falcons with the Wolfs. When Ulric Kerensky became the new ilKhan he deliberately use this to his advantage to sabotage the Crusader Clans efforts. He assigned Clan Steel Viper with Jade Falcons, the Falcons dislike the Vipers as much as the Wolves, and Clan Nova Cat with Smoke Jaguar, who also dislike each other.
This is a prominent theme in StarCraft. Particularly the first Terran campaign, which is almost entirely about humans fighting each other, rather than fighting aliens. The Protoss Judicators are also more worried about the Dark Templars than they are about the Zerg. The dominant force at any moment is the faction that is able to act as a unified team without infighting. Not even the Zerg are immune.
This happens in the GDI campaign of the original Command & Conquer. Partially due to propaganda made by Kane, the United Nations temporarily cut military funding to the GDI. For a few missions, the commander is left on his own to fight without vital base structures.
A little distraction like, lets say... a fullscale alien invasion is not a reason for Nod and GDI to quit fighting each other. This caused some irritation by the aliens, calling humans "warlike to the extreme". However, neither the GDI nor the aliens knew that it was all according to Kane's Evil Plan.
In the fourth game, Kane actually joins forces with GDI (for his own purposes, of course), offering them the blueprints of a "Tiberium Control Network" that can control Tiberium and save Earth from certain ecological collapse. Everybody promptly loses their shit over the decision, leading to a three-way war between GDI (with some of Kane's loyalist supporters), GDI (a breakaway faction under Colonel James), and Nod (another breakaway faction, led by Gideon, yet another of the 'Kane isn't really the Messiah, I am' line).
In Mass Effect 1, Ambassador Udina tries to stop you from saving all life in the entire galaxy from certain destruction because it might damage humanity's reputation (granted, he didn't believe you were telling the truth, but still).
Shepard can level this accusation at the Illusive Man in Mass Effect 3, calling him out on his descent from quasi-heroic Doing What He Had To Do to out-and-out attacking the Alliance at a critical time. Despite his efforts to brush aside Shepard's allegations, it's clear he doesn't really care, mostly because he's indoctrinated. Conversations with Javik and the AI Vendetta suggest this is pretty common where Reapers are concerned; they had a similar faction in their own politics which prevented them from deploying the Crucible.
In the vanilla game, the Alliance and Horde are in a cold war, but that does not stop either side from having adventurers(i.e. players) screw with the other side. When C'thun shows up and kicks off the Old Gods plan to kill the planet, it is only because they worked together did they stop Crisis #1. Once that's dealt with however, it's right back to screwing the other which starts Crisis #2 through #4.
Burning Crusade brought Crisis #2 which opened the Dark Portal to Outland and an invasion from the Burning Legion. The Alliance and Horde team up and push them back, then once they get through the gate the first thing they do is screw the other side over. Because they are so busy screwing each other, they do not deal with Illidan Stormrage, and that falls to the Sha'tar and adventurers to deal with that threat. When Kael'thas goes all Burning Legion, the Sha'tar form the Shattered Sun Offensive which was comprised of both Alliance and Horde and they successfully averted Crisis #2 until..
Wrath of the Lich King where Crisis #3 takes center stage. At this point, World of Warcraft takes this trope and goes ham: the the Alliance and Horde weren't fighting each other at first, they just thumbed their nose while they actually dealt with the Lich King. Then rebel Forsaken kill both the Alliance and Horde troops at the Wrath Gate, then the Alliance invaded Undercity in an attempt to take back Lordaeron while the Horde was in disarray, then King Varian Wrynn and Garrosh Hellscream got into a fight and open war was declared, while they were already fighting a war against the Scourge.. This led to the Broken Front, where the Alliance was beating Scourge forces, only to be attacked from behind by the Horde, who was in turn slaughtered by the Scourge giving the undead two battlefields worth of troops in one victory. Meanwhile, the Argent Crusade, realizing that the Lich King would not fall to a world divided, decided to host a friendly jousting tournament designed to get the Alliance and Horde to work together when the time came to assault Icecrown Citadel, but this ended up being all for nothing because the two factions ended up fighting each other again in a gunship battle. The Lich King would have won the final battle if it were not for the intervention of Tirion Fordring and Terenas Menethil's ghost. And it should be pointed out that while the paladins and death knights of their respective organizations don't get along perfectly well due to their contrasting motivations and methods for their fight against the Lich King, they are able to work together.
Cataclysm shows up Crisis #4 & spends a large portion of time on the very costly and devestating war Garrosh Hellscream is waging against the Alliance, and not the giant pissed off dragon that wants to end the world. Various lesser factions end up pulling most people's heads out of their asses and avert the end of the world.
And finally Mists of Pandaria, where the Horde under Garrosh's leadership is falling apart because everyone started to notice how big of a prat he was. Garrosh's warmongering, disregard for all life that isn't an orc, and his love of Kick the Dog tactics have caused the Horde to fall apart, while the Alliance solidify their unity and took advantage of the fracturing Horde which will eventually lead to a two sided invasion of Orgrimmar to end Hellscream's rule.
In Suikoden Tierkreis, this plagues the Magedom of Janam. The Mage Forces are led by Danash VIII's first wife, Shairah; their Arcane Acadamy is headed by his second wife, Rizwan. Then there's the Blades of Night's Veil, commanded by Chrodechild, who Danash wants to take for his fourth wife — yes, there's a third, who complicates things even more without her own command... Needless to say, they have problems withoutThe Order of the One True Way breathing down their necks.
Arcueid seems to have little issue with cooperating with the Church when necessary. They, on the other hand, feel differently as she's technically a vampire as well. Fortunately, she's essentially indestructible so they decided 'Fuck it' and agreed to work with her on occasion. That's mostly background material due to our only seeing sane Church members, but Ciel and Arcueid also have a funny tendency to start fighting to the death when differences arise. And they're friends.
Dragon Age: Origins takes this trope and runs with it. At the end of the first (non unique) chapter, Loghain ditches the battlefield and lets the king die - along with all but two or three Grey Wardens. The Wardens themselves are then persecuted from one side of Ferelden to another, even as the darkspawn steadily devour the countryside.
Worse, a civil war starts when Loghain basically shoves his own daughter and the queen off the throne as her "regent" and more than a few of the nobility take offense to this, as the King of the Ferelden must have the support of the Bannorn and Loghain isn't even in line for the throne. It also helps (?) that Loghain doesn't believe that a Blight is occurring and thinks the Wardens (who know that a Blight is happening) are enemy agents from a country that occupied Ferelden and ruined his childhood. Since Loghain is a war hero that freed Ferelden from said country a lot of his supporters follow him even as he grows increasingly paranoid and commits greater atrocities to protect his nation.
Used to great length in Dragon Age II with multiple factions warring against one another. The templars and the mages fight constantly, even though they should be working together to help everyone in Kirkwall. Members of the Chantry oppress the qunari, who in turn try to overtake Kirkwall in disgust. This even occurs with members of player character Hawke's party. If Hawke picks a side in the final act and the party members on the opposing side don't have their friend or rivalry meter high enough, they'll leave the party. In some cases, they may even try to kill Hawke.
Pokémon Gold and Silver has your rival. He hates Team Rocket beacause Giovanni was his father and after Team Rocket was defeated by Red, Giovanni left him and he blames Team Rocket. But on the other hand, he absolutely hates the player character, pushing them around, and even taking off your disguise while you're Dressing as the Enemy. He's actually the worst rival; Kanto's rival says things like "Smell ya later!", Hoenn's rival is a pretty good friend, and Sinnoh's rival is your best friend.
In Infinite Space, Yuri points out this is the reason why the SMC nations fell into Lugovalos' hand so easily. To elaborate, Elgava was far too confident with its military strength, and both Kalymnos and Nova Nacio were more concerned with their long-running bitter hatred to each other. And in Act 2, the LMC nations almost made the same mistake...
Yet another Warhammer 40,000 example is in the Dawn of War series, which contains five different campaigns (so far) in which everyone would much rather kill everyone else than work together to defeat the Orks, Necrons, Tyranids, and/or Chaos that are rampaging everywhere. This ranges from Winter Assault, in which the Imperial Guard and Eldar briefly ally before arbitrarily betraying each other, to Soulstorm, in which three different divisions of the same faction are pounding at each other.
It gets lampshaded repeatedly in the sequel, especially the Retribution expansion, as you can hardly go two plot-centered missions without someone calling out their same-side enemies on how there's such a bigger issue at stake. The Space Marines deal with the obfuscating Senator, they end up fighting themselves when Chaotic corruption begins to infiltrate their ranks, they have quite a few bitter issues with the Guard, the Eldar want to wipe out the entire planet rather than fight WITH the Imperium against the Tyranids, etc. Ironically enough, only the Inquisitor (the one usually most hell-bent on driving wedges between factions) seems willing to use cross-faction Alliances, even enlisting the Orks as mercenaries during their campaign.
This is the plot of the third Spec Ops mission in Marvel Avengers Alliance. Five of the X-Men got possessed by the Phoenix Force and wanted to use it to save mutantkind. The Avengers, on the other hand, were of the opinion that the Phoenix Force Is Not a Toy, and that it would end up wiping out the entire planet, mutants and all. And while they were at each others' throats, the bad guys were trying to turn the situation to their advantage. This even turned into a gameplay mechanic; you had to choose whether to side with the X-Men or the Avengers each time you started a mission, and you weren't allowed to use core members from the opposite side during fights or deploys.
The Syndicate soon fractures when the Red Skull was resurrected, who then proceeded to attack mutants, even those in Syndicate.
The Light Warriors of 8-Bit Theater spend lots of time trying to kill each other. Word of God has said the monsters and obstacles that they face in the world are nothing compared to the monsters and obstacles within the party.
In Worm, when Scion kills off half the world's population and many of the most powerful heroes sent to stop him, various groups decide to fight amongst themselves believing it's hopeless to resist.
The American military in Justice League Unlimited spends so much time making superweapons to defend against/destroy the Justice League, they completely ignore the fact that relying on Lex Luthor as opposed to the people who are busy saving the world every day might actually be a bad idea.
To be specific it was because of Project Cadmus's idea in recruiting villains to do their work for them.
The finale of the Cadmas arc is called "Divided We Fall".
In Avatar: The Last Airbender , Long Feng, the Evil Chancellor and default ruler of Ba Sing Se (the capital and last major outpost of the Earth Kingdom) refuses to aid and actively hinders Avatar Aang, The Chosen One, in the fight against the Fire Nation. After his manipulations are exposed and he's jailed, his Dai Li help him orchestrate a coup from his cell. But he is being played by a greater Chessmaster, Fire Nation Princess Azula, who gains the Dai Li's loyalty and uses them to sabotage the city's defenses. End result?
Earth King Kuei: The Earth Kingdom... has fallen.
On a larger scale, this has played out in the war as a whole. The Fire Nation launched an overwhelming strike against the Air Nomads, managing to commit genocide without any other nation coming to their defense (at least successfully). The Water Tribes and Earth Kingdom then decided to see to their own defenses, with the Southern Water Tribe only coming to the Earth Kingdom's aid 97 years into the war.
The Southern Water Tribe had been enduring constant raids by the Fire Nation for sixty years before the beginning of the show, so they had their own problems to worry about. The Northern Tribe, though? No excuse.
A classical parable concerning this is about the sons of king (I think) Attalus of Pergamon (although similar motifs seem to reoccur about a lot of different people) and his large number of sons. As they were squabbling over who would succeed him, he took a bundle of spears and asked his sons that whoever could break them could succeed him. No one could. The king then took each spear in turn and broke it easily, making a point about unity being strength.
Also shows up in King Lear and its most famous adaptation, Ran. Subverted in that the daughters of Lear/the sons of Lord Ichimonji don't learn the lesson and things get much worse.
Parodied in a Lineage 2 comic where an orc father tries to teach his quarreling sons this lesson... but is stronger than he thinks and easily breaks the united spears. He makes the best of it and converts it into a lesson in the importance of overwhelming strength.
The metaphor for this "strength through unity" approach is visually symbolized by a bundle of sticks often including an axe and is called a fasces. It is commonly found in art and heraldry all over the world. Its use has lessened somewhat after Mussolini adopted it as his symbol and named his ideology after it, but unlike another symbol we could mention, it is still fairly easy to find, particularly in the United States (where the old national fondness for Roman imagery and the institution of federalism make the fasces an opt symbol) and France (they're on the semi-official arms of the Fifth Republic).
A warning against this was attributed to Benjamin Franklin at the signing of the Declaration of Independence: "We must all hang together, or assuredly we will all hang separately."
Extremely prevalent trope in the military: every organization has some degree of political infighting and factionalism. Patton himself said that 'Competence in the battlefield is a myth. The side who screws up the least wins.'
This was the reason the republicans lost in the Spanish Civil War. While the fascists were all united and had a well-defined leadership and chain of command, the republicans had many factions. The Trotskyists allied themselves with the Anarchists because they thought the Revolution needed to come along the War (on grounds that not doing so would be the reason they would lose, just as the German revolutionaries had). The Stalinists thought that they needed to win the war first and then implement the Revolution. However, despite their ideological differences, the Stalinists openly persecuted the Trotskyists and the fact that their factions split further between Stalinists, Trotskyists, Anarchists and democrats meant the fall of the Republic and the rise of Franco's regime.
This is also the reason why the Nazis arose in the first place. Quoting the International Socialist Review: Again and again [Trotsky] called for a united working class action against the Nazi movement. The reformist SPD —the largest working-class based party in Germany— feared mobilizing its rnks against Hitler, preferring parliamentary manuevers and appeals to the state instead. Trotsky argued that the the Communist Party (KPD)—which alone still did not have the forces to defeat Hitler— should propose a United Front with the Social Democrats (SPD) for the purposes of physically confronting the Nazis. Such a policy would have been gladly supported by rank-and-file workers of all political shades, would have exposed the Social Democrat’s half-heartedness and would have stopped Hitler in his tracks. Sadly, the KPD followed a completely opposite strategy. Under the directives of Stalin, the KPD leaders refused to call for a United Front with the SPD, whom they insanely considered to be the “moderate wing of fascism” [social-fascism]. This policy paralyzed the working-class movement and allowed Hitler to take power without a fight. This disastrous strategy is what led the union leaders, party directives and congressmen of both the SPD and KPD to the concentration camps.
Another example, although this time it applies to the bad guys: towards the end of World War II, prominent Nazis were tearing each other apart to succeed Hitler, despite the advancing Allied and Soviet armies. This continued until the literal last days of the war.
The Byzantine Empire indulged in this all too frequently. Internal political squabbling at the Battle of Manzikert whilst on the battlefield with the enemy was a major cause of the Byzantine defeat there. Their army was almost destroyed, and the Empire never fully recovered. A century or so later, after Constantinople was conquered by the Venetians and their allies during the Fourth Crusade, the three Byzantine kingdoms that formed from the remnants of the Empire spent more time fighting each other over the Imperial title than trying to take their city back. All the squabbling between Christian Balkan states pre-Turkish conquest partially fits this trope.
Perfect example was Serbian Empire a powerful state in Middle Ages Balkan, with a modern Code of Law...But after death of strong Emperor, it was conquered by Turks, because it Land Lords couldn't unite and were in fight about who will be new Emperor. It resulted in 5 centuries of bondage under Turks(well actually Turks only controlled Southern parts of today Serbia, the Northern and Central parts were under Turks only for 219 years)
An absolutely perfect example is the Battle of Arausio circa 107 BC. Two Roman armies were raised to stop the advance of the Three Germanic Hordes (Teutones, Cimbri, Marcomannii), one led by a Patrician, and one by a Plebian. The Patrician, Quintus Servilius Caepio, absolutely HATED his counterpart, to such a degree that he refused to go along with his plans to merge the two armies as one and wait for the German attack. Caepio kept his army separated due north of the other army, and when the Germans came, they swarmed over his army and utterly crushed it, then waited a short time before swarming over the other army next. Nearly 100,000 Roman soldiers and camp followers were killed, nearly twice as many as the Battle of Cannae.
Even when the Imperial Japanese Army was rampaging out from Manchuria into the rest of China, the Chinese Nationalists and the Chinese Communist forces often spent more time fighting each other than defending against the invasion.
Lord protect me from my friends, I can handle my enemies myself.