Divide and Conquer

""Siamese fighting fish - fascinating creatures. Brave, but on the whole, stupid. Yes, they're stupid. Except for the occasional one, such as we have here, who lets the other two fight. While he waits. Waits until the survivor is so exhausted that he cannot defend himself, and then like SPECTRE... he strikes!""

- Ernst Stavro Blofeld, From Russia With Love

Why work when you can get someone else to do the work for you? A favored tactic of The Chessmaster, both villain and Anti-Hero, is to get two of your enemies to fight each other instead of you. If one wins, he should be weakened enough from battle that you can knock him off before he recovers.

Most often, this is when the villain decides to let another, unaffiliated villain absorb the majority of the Hero's time and energy. Truly skilled use of this trope is when the villain can break up the Five-Man Band.

The Power of Friendship is a powerful thing. Some villains realize that after getting beaten by it too many times, so they try to somehow split up whatever team of heroes they're facing. This might involve getting two heroes to hate each other, getting one hero to hate the others, or otherwise forcing the team to split up. The Lancer is a common target of this tactic.

On the opposite side, it's the usual hero tactic when their enemies try working together. Of course, they're usually much easier to divide, since not only they lack The Power of Friendship, but they're probably already planning to double-cross each other anyway. By contrast, when the villain sets two groups of heroes against each other, they're much more likely to figure it out and team up.

Compare Let's You and Him Fight. Contrast Enemy Mine. #9 in The Thirty-Six Stratagems, making this one of The Oldest Tricks in The Book.

Anime & Manga

 * This is the goal of Yugi in Tenchi In Tokyo.
 * In the Yu-Gi-Oh manga's "Death-T" arc, one of the challenges is a room being gradually filled with huge falling blocks. It's intended to force the heroes to think only of themselves rather than trying to save their friends.
 * In Monster, one of Johan's most common strategies is to get different groups of people to fight against one another.
 * Naraku from Inuyasha tried several times to put Sango against the others by threatening the life (or some such) of her little brother. The first time he managed to make her steal Inuyasha's Tessaiga, but she's gotten wiser since. He also uses various tricks to physically split up the team so he can take them out one by one.
 * Team Rocket uses this plan a few times to catch the Pokémon of the episode and almost get away with it until the last minute.
 * The strategy Schneizel uses twice on Lelouch:.
 * The description above says "contrast Enemy Mine", but in Soul Eater, Medusa actually managed to Divide and Conquer by means of Enemy Mine. And although she didn't tell them, the people she was "helping" found it obvious that this is her plan.
 * In Baka and Test, Class F utilizes this against Class A during a summoner war. They use favors gained from defeating the other classes, or deception in the case of Class C, to have them wear down Class A before the fight. Class F nearly succeeds with it, until the school starts to break down, causing the Class F rep to be distracted momentarily.
 * Aizen's plan in the Soul Society arc incorporates large amounts of this. He has Ichimaru let Ichigo's crew escape, so the thirteen squads spend their time and energy fighting them. At the same time he manipulates Rukia's execution to cause splits within the thirteen squads, and after faking his own death manipulates Hinamori into attacking Ichimaru, Kira and Hitsugaya. All of these things manage to divert attention from his machinations, and if it wasn't for Ichigo doing a little better than expected and Captain Unohana realising something was wrong with his 'dead' body, Aizen's plan would have succeeded, he would have escaped scot free and a significant amount of his enemies would be dead.

Comic Books

 * The Civil War pitted Anti-Registration Superheroes versus Pro-Registration Superheroes. At the end, the Pro-Registration were so weakened and so morally confused they were easy pickins for the Skrulls. And that ended up with the superheroes so paranoid, they ended up going at each other's throats again. At the end, the "winners" were so devastated that the supervillains end up taking over the United States.
 * Bane, of Batman extraction, is legendary for this. Aware that he couldn't take Batman in a straight fight, he instead released dozens of inmates from Arkham Asylum, leading Batman to run himself ragged for months until Bane showed up in the Batcave and "broke the Bat."
 * In one issue of Incredible Hercules Malekith combines this with Let's You and Him Fight to weaken both Hercules and Thor sufficiently that his secret weapon will be able to defeat them easily. His plan fails ignominiously due to him not being aware that Zeus was standing right there when he sprang this trap.

Films -- Live-Action

 * This is a key element in A Fistful of Dollars
 * A Fistful of Dollars got the plot from Kurosawa's Yojimbo which in turn got it from a 1930 gangster film called Roadhouse Nights which was based on Dashiell Hammett's novel Red Harvest.
 * The same plot was used in the western Django and Last Man Standing.
 * Used in Serenity, where Mal pits against each other to buy enough time to.
 * And in Lucky Number Slevin, which is unfortunately a huge spoiler.
 * James Bond has a lot of it. Three deal with USSR x USA, From Russia With Love - source of the page quote -, You Only Live Twice and The Spy Who Loved Me (first two are Blofeld-lead SPECTRE).
 * Tomorrow Never Dies has the villain trying to get World War Three between the UK and China, just to get broadcasting rights in the latter.
 * This also seems to be QUANTUM's strategy in the new movies: get Bond so paranoid about his superiors, and so confused by the abrupt shift into a World Half Empty with a Black and Grey Morality, he ends up failing to defeat them.
 * Also, the Joker's strategy: get Batman so riled up with the Black and Grey Morality, fighting the police and trying to redeem Harvey Dent, he can barely take on the Joker.

Literature

 * May not be entirely accurate, but Mordeth in The Wheel of Time seems to have managed to pull this on an entire city.
 * In Outbound Flight, this is sort of what Commander Thrawn did. Sort of. Due to his Batman Gambit, the entire Vagaari fleet came out of space near where Outbound Flight was trying to decide what to do about him. The Vagaari being probably the most unambiguously evil side Zahn has ever written, they attack Outbound Flight, and the Jedi at its weapons stations sense the Living Shields on the outsides of the ships, so they use the Force to more or less scramble the minds of the Vagaari. Then Thrawn triggers the second programming level in the droids he'd arranged to be on the Vagaari ship so that they slaughter the Vagaari high command, while also cuing the droid starfighters to buzz the Vagaari ships and shoot between the hostages. Being in such close contact with beings being slaughtered en mass, the Jedi are stunned and can't react in time to prevent Thrawn shooting out all of the weapon stations, killing most of them.
 * Outbound Flight wasn't his enemy in the same way that the Vagaari were, even if its commander took an instant hatred to him. If that commander hadn't been a budding megalomaniac, or if Thrawn hadn't followed his standard policy of shooting out the weapons systems of anyone who he distrusted but wasn't all-out enemies with, the major problems probably would not have happened.
 * In the first Conqueror book, Wen Chao keeps up hostilities between the Mongols and Tartars to keep both sides weak and thus allow the Chin to extract tribute from them. Unfortunately for him, the Mongols manage to win the war under Temujin, who quickly ends the practise.
 * In the second book, the Chin emperor refuses to send aid to Emperor Wei of Xi Xia when the latter is attacked by the Mongols, specifically saying that it's better for one's enemies to fight each other.
 * The entire point of Tom Clancy's The Sum of All Fears, where Arab nationalists (neo-Nazis in the film) nuke Denver (Baltimore in the film) in order to start World War Three between US and USSR (Russia in the film). It nearly works, despite the fact that there is no reason to suspect the Russians given the lack of a missile launch. Of course, in the film, the neo-Nazis do follow up by tricking Russian pilots into bombing an American warship.
 * And they do follow up in the book as well, only instead of bribing an air force commander to attack a U.S. Ship, they pose as officers in the red army and trick a tank brigade in East Berlin into attacking an American base in West Berlin. They are also unwittingly helped by an American mole in the Politburo whose been feeding the U.S. false information in the hopes of destabilizing the current government in the USSR so he can grab power himself.
 * Inverted in the Asimov's short story: In a Good Cause. where the wars amongst humans actually made them stronger, which gives them the upper hand against the united aliens.
 * Also inverted the same with the aliens of Harry Turtledove's Worldwar (Literature) series, as their millennia-old unifications means their technology has been purposely stagnated by the government to prevent disruptive changes in society, while humans being disunited and constantly at war with each other means we're able to change much quicker.

Live-Action TV

 * Buffy the Vampire Slayer: Spike (inspired by The Beatles) tries it at the end of Season 4 at the behest of the Big Bad Adam. Unfortunately, another part of Adam's plan involved them sharing information. So he then had to convince them to talk to each other again, whereupon they reconciled.
 * This is the official motto of a league of assassins, the Order of Taraka.
 * The number of times they've done this in Power Rangers is beyond counting. Often more than once in the same season.
 * Michael pulls one of these about every third episode of Burn Notice.
 * The Twilight Zone episode " ", aliens do this, taking advantage of the fact that Humans Are Bastards. End result: mass hysteria. Cut to two Human Aliens on a hill overlooking Maple Street, marveling at how they won't have to fire a single shot, the humans can easily be tricked into killing each other!
 * The whole thing, of course, was an allegory for the McCarthy witch hunts.
 * In Stargate Atlantis, McKay reactivates the Replicators' programming that causes them to attack the Wraith. Unfortunately, it backfires a bit when the Replicators determine that the most efficient way wipe out the Wraith is to eliminate their food supply.

Myths And Folklore

 * One of Aesop's fables tells of a lion who was unable to hunt down a herd of cattle since the cattle would always stick together as a group. That is, until the lion gets the idea of spreading gossip among the cattle to get them to fight and seperate allowing said lion to attack the cattle one by one.

Tabletop Games

 * Any good Risk player has done this.
 * Friend Computer would like to remind all citizens that this is an effective way of dealing with commie mutant traitors. Also that knowledge of such techniques is treason.

Theatre

 * In The Golden Apple, Ulysses invokes this tactic by name, splitting the people of Rhododendron on the issue of Helen to win her back from them.

Videogames

 * Very common tactic players use in video games that allow NPCs to fight each other, such as Half-Life (letting Combine fight Zombies, HECU to fight aliens) and Halo (letting the Flood take out the Covenant). It can be traced back at least as far as Doom, where "monster infighting" was crucial to beating some parts. Doom 2, for example, has a Spider Mastermind and a Cyberdemon right next to each other. The only effective way to survive is to get them fighting each other.
 * attempts to do this in the first Advance Wars. He tried to get the nations of Orange Star, Blue Moon, Green Earth and Yellow Comet to engage in a brutal war that would leave all sides devastated, so he could sweep in with his own forces and conquer all of Wars World.
 * Kerrigan does this to  in Starcraft Brood War.
 * Devil May Cry 3:.
 * Any Pit player worth his weight in salt does this as well when deploying Palutena's Army in Super Smash Bros Brawl. It's one of the few Final Smashes that allows the user to move and act freely with his own moveset during its execution. The reason it falls here is that the Centurions are dangerous in their own right, and the player has to choose to either focus on dodging them or dodging Pit, though a skilled player can do both for the most part.
 * By the end of Kingdom Hearts II, Sora is too busy dealing with the Nobodies and Organization XII to properly deal with Maleficent, Pete and the Heartless.
 * Ace Combat 5 has this as the driving force behind its plot. 15 years before the game began, the country of Belka tried to take over the world and failed, eventually setting off 7 nuclear weapons on their own cities to stave off the approaching allied forces that included Osea and Yuktobania. In the present day, Yuktobania attacks Osea, and the two are plunged into a bitter war that drags on until nobody can remember why they're fighting. After the player's squadron is betrayed, the truth is revealed:
 * An element of gameplay in Final Fantasy XIII. Because of the different alignments enemies can have (Cocoon monsters, Pulse Machines, Pulse Monsters), occasionally the player will find two factions of monsters fighting each other. They can then fight the stronger enemy alongside the second enemy, then when the first enemy is defeated, the second enemy is weakened.
 * In Silent Storm, Thor's Hammer is trying exactly that with the Allies and the Axis. While they didn't start the war, they are taking advantage or it by supplying both sides with advanced weapons, while keeping the best goodies for themselves.
 * In Haegemonia: Legions of Iron, the Darzok use this method to break up their enemies. They convince a Kariak general to rebel against the Human-Kariak alliance, allowing them to build up their forces while the Kariak fight among each other.
 * Probably one of the better ways to deal with enemies in Bio Shock, particularly the Big Daddies. Just casually goad a Splicer into attacking you while you're standing near one of the lumbering Daddies. More than likely one of their attacks will hit him instead of you, and after that you can honestly just slide on over to the sidelines while they go at each other.
 * In The Elder Scrolls V Skyrim, this is what the Thalmor's tactics are presumed to be . In the Great War, the Thalmor, fought to a standstill by the Empire, made a peace treaty with terms that the provinces would never agree to (ceding half of Hammerfell and outlawing Talos worship). As of the time of Skyrim's story, Hammerfell has seceded from the Empire and Skyrim erupted into civil war, meaning that the Empire is now a much weaker target. Despite this, they don't want
 * In Neverwinter Nights 2, there is a section where a group of Fire Giants want to kill a nearby Dragon and the Dragon wants to kill the Fire Giants that have been harassing it. They both request your aid to deal with the other, and they both have something valuable that you may wish to take (for the Fire Giants, it's a quest item. For the Dragon, it's a massive pile of gold). No matter who you ally with, in the end you're given the option to betray both of them and let them duke it out with each other. Whichever side survives will be in a weakened state, thus allowing you to easily finish them off.

Webcomics

 * Happens all over the place in The Order of the Stick. First you have the Inter Fiend Cooperation Commission, who seek to keep the battles between The Order, The Linear Guild, and Team Evil going as part of their Gambit Roulette. On a smaller level, General Tarquin is poised to take over the entire Western continent this way. In an inversion, he's going to keep the continent split amongst himself and his confederates so that no one country is seen as a threat or a tempting prize.

Web Original

 * In The Gamers Alliance, the mage Jemuel plays both the Grand Alliance and the Yamato Empire against each other during the Great War in order to carve his empire while the two are busy fighting. He succeeds, crushes the remaining Yamatian troops in the kingdom and frames the Alliance in the eyes of the populace for causing a catastrophe which has devastated a part of the continent.

Western Animation

 * Thunder Cats partial example: in one episode Lion-O is bodyguarding some old peasant and fights off an attacker, who turns out to be Tigra. And the peasant turns out to be Mumm-Ra, who told Lion-O that a thief would attack him and told Tigra that a thief was following him. The end result was that Lion-O's magic sword was broken because he battled a fellow Cat.
 * Grodd did this with the Justice League in "Secret Society".
 * Also in Justice League, we are treated to a Crowning Moment of Awesome when
 * Shego manages to pull this off in the Kim Possible Made for TV Movie "A Sitch In Time" by having Ron's mother get a job that requires their family to move.
 * Done (as a reference to the Beatles, once again!) in an episode of Powerpuff Girls.
 * Not only was this the plot of the first episode of Teen Titans, it was also the title!
 * In the Filmation film, Flash Gordon: The Greatest Adventure of All, this is how Ming keeps control of the planet Mongo, although they phrase it as "separate and rule".
 * Discord in My Little Pony Friendship Is Magic splits up the Mane cast physically when they enter his hedge maze. He takes the opportunity to Mind Rape them one by one to split up their friendship as well.

Real Life

 * Divide and Conquer has been a tried and true tactic of empires throughout history. The Other Wiki has a more comprehensive explanation of Divide and Rule and its uses.
 * This was the favorite tactic of Julius Caesar, arguably the Trope Namer. His motto was Divide et Impera, which translates to "Divide and Rule" . Caesar would ally with one tribe in Gaul (modern France) and pit them against others to win. This was the reason the Gauls lost, or at least it sure helped.
 * This has always been characteristic of Roman conquest, since their early wars within Italy. Once conquered or "allied" a city-state would be bound by contract to Rome and forbidden to form any kind of alliance (including marriage) with their former allies. By the time Rome controlled the whole of Italy, they had over 150 contracts with various states, none of which had any formal links to one another other than as allies of Rome.
 * The war between the Eastern Roman Empire and Sassanid Persia that took place from 602 to 628 weakened both countries so much that the Arabs were able to invade and conquer all of Persia and half of the Eastern Roman Empire. The Arabs did not actually instigate the conflict, as they were still a disorganized bunch of tribes, but they took advantage of the situation, being united under Islam soon afterwards.
 * This is also the primary reason that tiny expeditions of conquistadors were able to singlehandedly obtain victory over entire American subcontinents, by sowing confusion and playing different native powers against each other.
 * Smallpox and Guns probably had a lot to do with that too, but it was at least a big reason.
 * Smallpox, yes. Guns, not so much. Thrown spears, arrows, and slings were superior to period firearms in terms of rate of fire, accuracy, and ability to produce and repair. The main advantage guns had was the psychological one from the boom, and that was largely canceled out due to the vast numerical superiority of the natives. Pitting the various tribes against each other (by convincing them that the sun would still come up if they didn't let the Aztecs cut out their hearts, for instance) was the key to victory.
 * Jiang Jieshi's schtick, and that of his eventual rival Mao Zedong. Both were shrewd and calculating politicians, and used this strategy to great effect as they bribed, back-stabbed, assassinated, out-cliqued and out-manoeuvred their rivals in their scrambles to be the top dogs within their party-factions-governments. Likewise they maintained their power in this way: both played on factional rivalries to safeguard their own positions. The problems with this kind of government became apparent during the course of the post-WWII Civil War when Jiang's paranoia, heavy workload, and military incompetence came to a head: when taken with Jiang's poor administration and strategic decision-making, the Army's lack of co-ordination - due to factional rivalries and the resultant lack of coordination between Armies, Divisions, Brigades and sometimes even the Battalions within them - proved fatal. Once Mao's armies broke his line at the Yangtze and swept into South China, the majority of Jiang's remaining forces defected or simply melted away. For his own part Mao learned not to tolerate any kind of factionalism within the Army, though he continued to Divide and Conquer his political would-be/could-be/might-be rivals well into the senility of his old age.
 * The Dutch, French and English East India Companies had low (think 10%) and ever-decreasing numbers of European personnel which eventually, after the Sepoy (Indian Soldier) Rebellion of 1857 resulted in the English East India Company being dissolved and and replaced by the British Raj, which directly administered two-thirds of the subcontinent's territory and population with an Indian Civil Service of no more than 2000 men. Only the very top level of the administration was British, and the remaining third of the subcontinent was governed by states loyal to the British Crown
 * A literal example occurred during The American Revolution, when Britain tried to take over the Hudson River valley in order to physically cut off New England from the rest of the Thirteen Colonies.
 * Bismarckian Germany did the same thing in the late 19th century, keeping France isolated from their natural allies, Russia and the UK.
 * Red October and the fall of the Czarist and Provisional Russian governments was effectively due to Germany successfully using public discontent to undermine the power of the Pro-Allies factions in Russia in the hopes of reaction against them that would open the door to a German-dominated Eastern Europe.
 * One of the reasons Japan was able to conquer large portions of China in the 1930s - the Communist Chinese wanted their own government defeated even more than Japan did, while the ruling Chinese Nationalists were conversely so preoccupied with trying to stamp them out (not to mention being hopelessly corrupt, incompetent and unpopular-those going together) they caved easily before the Japanese.
 * The German-led Axis took advantage of this during their invasion of Yugoslavia in WWII by rallying the country's neighbors to help invade and by arming the radicalized minorities (most notably the Croats with some Slovene, local Hungarian, and Albanian support) against the Serbian-dominated Royal government. It worked devastatingly well - probably too well, if the subsequent bloodshed and the resulting rise of the Partisans and the Chetniks and their effective tying up of hundreds of thousands of Axis troops shows. Some of the Croatian groups the Nazis stirred up were also such fanatically brutal killers that even SS death squads were sickened by them, and left the Serbs burning for revenge...
 * The Soviets tried to do this throughout their history (and started before the Soviet Union even existed yet) by trying to drive wedges between their enemies, whoever they might be at the time. In World War One, they tried to pull Germany, Austria-Hungary, Bulgaria, and the various White Factions apart and incite revolution in at least one of them. Before, during, and after World War Two, they believed that pitting the West against the Germans would leave a power vaccum that would effectively cement Soviet dominance (which was thwarted by Hitler's paranoia and decision to strike at the USSR first). And in the Cold War they generally tried to keep the West and the Chinese from coming to any kind of agreement while trying to undermine the solidarity of the Western powers themselves.
 * This was countered by United States opening up (relatively) friendly relations with China despite their ideological incompatibility, as each considered the Soviets to be the greater threat (America seeing them as such because the USSR was simply more powerful than China, and China because the USSR was literally right next door to them).
 * Large companies have been known to do this as well. During the Great Southwest Railroad Strike of 1886, Railroad Baron Jay Gould allegedly boasted that he could "hire one half of the working class to kill the other half."
 * In recent years, divide-and-conquer has been used in Culture War politics by spin doctors such as Karl Rove and Lynton Crosby, in the form of 'wedge politics' (or dog-whistle politics in Australia).