A concept in international relations, but one with a lot of relevance in fiction.
To give a hypothetical example, you have five countries:
- A - a Great Power
- B - another Great Power, roughly equal and hostile to A
- C - a lesser power associated with A
- D - another lesser power roughly equal to C, associated with B
- E - another power (Great or lesser) that is neutral
A+C equals more or less B+D, so any kind of war between them would be indecisive or have an outcome that is hard to predict. A protracted war would be incredibly expensive, and bloody, to boot. It's in everyone's interests to prevent or limit A-B conflict.
However, if E decided to align itself with A or B, that trio could have a decisive advantage in a limited conflict (before the duo brings their full resources to bear). A protracted conflict between the five would be even more incredibly bloody and expensive than one between the four, however, and its outcome would still be in doubt despite the slight advantage held by one side. Furthermore, it might be in E's best interests to keep A and B balanced against each other, leaving itself free to steer an independent course as neither of the two would wish to drive it into the other's camp by behaving too aggressively against E.
The problem with these arrangements is that not all the powers involved will always have an accurate idea of the other powers' intentions or the relative strengths of all the powers. This can prove disastrous when a power decides to start a war because its leadership isn't in touch with reality.
- The One Piece 'verse has a Balance of Power crucial to the overall plot of the story. The type A and B greater powers consist of Marine Headquarters versus the Four Emperors, the World Government's military and the four most powerful pirate crews in the world, respectively. In the middle are the Seven Warlords of the Sea who, on paper at least, are a Type-C lesser power aligned with and aiding the World Government against the Emperors. However, almost all of them are carrying out their own agendas on the side and some of them have casual and even friendly contact with some Emperors and up-and-coming pirates, making them more of an Type-E neutral power in practice. Threats to this balance include single-minded pirates like Monkey D. Luffy and the deliberate actions of Dragon the Revolutionary.
- Late in the story, Naruto has revealed that the Tailed Beasts, the Bijuu, and their hosts, the Jinchuuriki acted as a balance among the various nations. Konoha and Suna, each having only one bijuu, allied with one another after the last war to deter Kumo and Iwa which both hosted two; Kiri's natural defenses and two bijuu allow it freedom in operation but it lacks the unity needed to take advantage of that. Taki's single bijuu and lesser standing make it an ideal buffer between Kumo and Konoha. Most of the lesser villages align with other villages, have treaties via their daimyo lords, or are located in places where attacks will spark retribution from neighbors. The existence of a free Bijuu would spur other villages to attempt to claim it and gain an advantage, thus necessitating its capture.
- Despite the long time it took to be introduced, this balance was eventually revealed to be crucial to Naruto's backstory. Because maintaining it was one of the biggest reasons that the Fourth Hokage sealed the Nine Tailed Fox inside of him.
- The Vatican Treaty in Rebuild of Evangelion dictates that no single country can have more than three active Evas at any given time.
- In Beelzebub, the balance lies in the hands of the Tohoshinki, the four strongest delinquents of Ishiyama High, who kept all the other delinquents at the school in check. When Oga defeated all four, he became the strongest delinquent at Ishiyama and united the entire school under his reign. Unfortunately, he destroyed the school not long after. This action would affect the later "Return to Ishiyama" arc, where due to the destruction of the school (which had to be reconstructed twice thanks to the "Akuma Academy" arc), Oga and the Tohoshinki were unable to keep all the other delinquents in check (the students of Ishiyama were spread out during construction), resulting in a power struggle, where over thirty groups are vying for the top spot, and aim on taking out them first. Essentially, the main goal of the arc is to put Oga on top again in order to get the school under control, and restore the Balance.
- In Aeon Natum Engel, the defences of Esoteric Order of Dagon-controlled Iceland are partly based on this principle; neither the New Earth Government nor the Migou can attack without weakening their position against the other, thus stopping them from taking the territory. Of course, the assumption that the NEG is after the Dagonite-controlled territory turns out to be painfully flawed.
- In Aeon Entelechy Evangelion the NEG and the Migou had a status quo for six years since the Fall of China, with no major morale-breaking loses for the NEG since then. Then Mot shows up and destabilizes the Eastern Front.
- Second Wind: While the overall arrangement is generally the same as it is in canon, the Straw Hats are technically a part of the balance (in this timeline) thanks to their alliance with Whitebeard. This usually wouldn't be a problem, except Luffy and Zoro, as time-travelers, are New World-grade pirates — and the world at large doesn't realize this until they manage to defeat Aokiji at Water 7. Pirates capable of such a feat are very scarce, even in the New World, and thus the Straw Hats have (unintentionally) tipped the balance in favor of the Four Emperors. This becomes a plot point later on, as the World Government is so desperate to restore the previous status quo that they are willing to throw the collective force of the Marine's entire top brass at the Straw Hats, up to and including Sengoku himself, to make sure they don't enter the New World and join Whitebeard's forces.
- Some of the intrigue in The Godfather comes from the families negotiating about this.
- The United States and the Soviet Union in Thirteen Days are the A and B. The biggest C's and D's in the movie are Cuba (whose hosting of Soviet missiles was the central issue of the movie) and Turkey (whose hosting of American missiles plays into the negotiations); other players include Chile and Romania (the UN Security Council meeting) and the rest of Latin America via the Organization of American States (unanimous vote in favor of the US "quarrantine"). China and India are also mentioned when the former instigated a border-clash over some mountains in the himalayas—though they don't play a role in the plot itself, their mention even when the Kennedy administration's primary focus was already on Cuba and the Soviet missiles there illustrates the breadth of scope the US had in its foreign policy during the Cold War.
- In The Third World War, the war starts because the USSR is worried about losing D (the Warsaw Pact) and is won by the West partly because of the role of two Es, namely Ireland and Sweden.
- Oceania, Eurasia, and Eastasia of Nineteen Eighty-Four; at any point, two are allied with each other, but the alliance always crumbles before the third is defeated because one of the two grows too powerful, and the alliances are reshuffled.
- Romance of the Three Kingdoms initially starts with a bunch of warlords carving out territory for themselves throughout China, but eventually the power consolidates around the three main rivals Cao Cao, Liu Bei, and Sun Quan. The balance sets in after the Battle of Red Cliffs, where the Sun and Liu factions put a large damper on Cao Cao's quest to reunify China.
- Isaac Asimov's Foundation Trilogy starts out this way. As the Galactic Empire starts to decline, the planet of Terminus is surrounded by the 'Four Kingdoms', who are looking to expand their own influence. They've also reverted to primitive forms of technology though, so when Salvor Hardin, the Mayor of Terminus, lets slip to one of the Four Kingdoms' ambassadors that Terminus still has nuclear power, it looks like Terminus is going to get invaded for its technology. Hardin, the Magnificent Bastard that he is, also let slip Terminus has nuclear power to the other three Kingdoms. None of the four kingdoms are willing to invade Terminus now, under threat of joint retaliation from the other three kingdoms.
- A Song of Ice and Fire or "How Can Seven Kingdoms Continue To Be United Without The Tyrants Who Welded It Into One With Violence and Diplomacy Still Being In Charge?" The answer for the Seven Kingdoms under King Robert Baratheon is... finding a new balance to replace the old proved a rather tough process containing more downs than ups. And, it only gets vastly more tricky as the series progresses. Permanent schism remains very much on the cards at every point, mainly due to the number of people vying for control while simultaneously trying to juggle everybody else. And, that's without Icy Doom coming from the North and Hot, Angry Dragons coming from the East to complicate things.
- The Silicoids in Sergey Lukyanenko's Line of Delirium are obsessed with the idea of universal balance. This is the core tenet of their culture, and it shapes everything from interpersonal relations to interspecies diplomacy. During the early stages of the Vague War, they took humanity's side in the conflict, as humans were getting beaten on all fronts. By the end, though, they decided that the new Human Empire was strong enough to keep up the Balance and left.
- In Vernor Vinge's The Witling, Thengets del Prou and Ajão discuss this at some length; the balance of power on Giri is tenuously equalized between three demographics. It's probably to be expected, considering that almost Everyone Is a Super. Any two of the major demographics could dominate the third if they united. Prou remarks that if the aristocracies and populace united against the Guild, the Guild would be destroyed, but at the cost of millions of lives. To elaborate:
"Ajão realized he was telling the literal truth. If a hundred-ton moon rock were exchanged for an equivalent volume of—say—air at Giri's surface, the net potential energy released would be equivalent to a small fission bomb. Perhaps that explained the strange glassy plain Draere had photographed in the southern hemisphere."
- The Guild, whose less-than-600 members are incredibly powerful but drastically outnumbered by the rest of the Azhiri, who number around four hundred million. Prou notes that "a single Guildsman can destroy whole cities", and with some quick mental calculations, Ajão realizes he's not boasting.
- The aristocracies, who command well-trained armies and defensive strategic locations.
- The rest of the population, who pose a threat through sheer numbers.
- The Dresden Files: The Summer and Winter Courts of the Fey have a cyclic balancing act. From the summer solstice to winter solstice, the Summer Court goes from the height of its power to weakest while the Winter Court goes from its weakest to its strongest. This is reversed on the other half of the year. This balance is kept because if one side were to overcome the other it would lead to the destruction of the world as it is. If Winter wins there will be another ice age. If Summer wins, then there will be an infusion of growth in all living things, from people, to plants, to deadly viruses. As a result, if one side tries to gain some outside power, then the other side will seek to stop that power or gain some equal measure of strength. In Cold Days it is revealed Winter has at least three times as many soldiers as Summer but they are out protecting all of Reality from entities from Outside Reality and who would destroy Reality if they had their way. Summer's forces are there to keep Winter from using the remaining portion to hurt humanity, as Mab, Queen of Winter, will sacrifice anything she needs to in the name of protecting Reality (herself included).
- This idea is always in the background of John Christopher's Sword of the Spirits trilogy, with the various post-apocalyptic English city-states all squabbling and skirmishing with each other, but avoiding outright conquering of rivals. This begins to break down as the series progresses although at the end, the protagonist predicts that it will be the looming return of 20th century technology that will truly destroy the status quo.
- One of the central themes of Babylon 5 is the galactic balance of power between Humans, Narns, Centari, Vorlons, Minbari, and the League of Non-Aligned Worlds. It starts off being about as equitable as might be reasonably expected, but naturally it all turns to custard by season 2.
- It's pretty much shown that the "balance" between the younger races is mainly due to political, religious, etc. choices by the more powerful races. While, Humans, Narns, and the League are roughly equal, Centauri technology is well ahead of them and the Minbari are even farther ahead to where the Centauri never tried challenging them even at their most aggressive. The real Balance of Power is between the Vorlons and the Shadows who far outstrip any of the younger races in power. They are the A & B of the story Their struggle is about how many C's and D's they can get to fight for their causes.
- Game of Thrones: The only way to stay in power is to maintain one of these. Before the conquest, the Seven Kingdoms were relatively stable despite frequent warfare because of this trope. Then Aegon the Conqueror broke the deadlock and united them using dragons. The Targaryens served as an Outside-Context Problem (from Westeros' perspective) for most of its near 300 years of reign. They held power by dragons but they also managed to keep a lid on all kinds of regional grudges and jealousies when they were in charge and they kept the Faith of the Seven on a leash, removing their militancy and curbing some of their most fundamentalist strains. Then the dragons died out and eventually Robert's Rebellion overthrew the Targaryens by uniting five of the nine factions against them. Then Joffrey's ascent annihilates the equilibrium into half a dozen warring factions, as there is a Succession Crisis and all the old problems come out - regional grudges, over-ambitious vassals, dislike between the North and the South and the far south as well as religious fundamentalism being back and all of them trying to go back to some ideal past before Aegon's Conquest.
- In Star Trek, The Federation, Klingon Empire, and Romulan Star Empire all see themselves as A with the other two acting as B and E at different times over the course of more than a century. Once other powers like the Borg and Dominion came into play, this balance fell apart. Section 31 made it its mission during DS9's final season to permanently tip the balance in favor of the Federation.
- This was the them of the TOS epsiode "A Private Little War". Kirk finds out the Klingons have started arming one group on a primitive planet. His only solution is to arm the other side to keep one from overwhelming the other. He chooses the possibility of perpetual hostilities over the genocide of one side.
- This also comes up in Star Trek: The Next Generation when a Starfleet captain resolves a Hostage Situation by illegally giving weapons to the hostage takers. He then gives the same weapons to the hostage takers' enemies to restore the balance — and this leads to decades of civil war.
- In Into the Badlands the Barons are warlords who control fixed territories and are each in charge of one main trade resource. The Barons do not really mind when one Baron is deposed through Klingon Promotion or even assassinated by another Baron. However, they take a grim view when one Baron seizes territory belonging to another Baron since this upsets the balance of power. When Baron Quinn goes to war against the Widow, he seizes her oil fields which immediately sets all the other Barons against him.
- Diplomacy is practically a research project into this trope. With seven A's and B's, whom can devolve into C's and D's as the game develops. And really skillful players could bring them back to A's and B's.
- Twilight Struggle has the US and Soviet Union as the A and B, with pretty much every other country on the board as potential C's and D's depending on who controls them. The only real E on the board is Communist China, who is represented as a card rather than a space that can be played by one of the powers for influencing other countries on the board (bonus if it's in Asia) and gets passed between each superpower once played.
- Battletech, after the Wars of Reaving only 4 clans remain in Clan space. Clan Star Adder-A, Clan Cloud Cobra-C, Clan Coyote-B, and Clan Stone Lion-D.
- Mass Effect has Treaty of Farixen, which determines how many dreadnoughts each citadel species may have. Humans, who are limited to 1 per 5 turian, decided to build carriers instead.
- Sort of subverted: All the powerful treaty signatories (Turian, Asari, Salarian and later Human) are closely allied and the only races that could possibly compete with them (e.g. the Geth and maybe the Quarians and Batarians) are outside the treaty, the purpose of the treaty is more about enforcing the unipolar power of the citadel council races than making any sort of balance of power.
- Final Fantasy XII has this as a major driving factor behind its plot. What triggers the game's main story is that the balance between two empires, the Archadian and the Rozarrian empires, has been overturned when the Archadian Empire annexes the E power Dalmasca and destroys another one, Nabradia, both of which also served as buffer states between the two empires.
- Three of the Ancients in Eternal Darkness have fallen into a precarious form of this, represented in-game as Elemental RockPaperScissors. Each seeks to destroy the one weak to their power and achieve ultimate power - all ignorant that the Dead God Mantorok saw this coming a long time ago and through three Alternate Universes tricks all three into killing each other.
- In Kill Six Billion Demons, the seven God-Emperor Demiurges negotiated an uneasy piece after a catastrophic Forever War, enforced by the fact that each one of them had the means to destroy any other. Now, the balance has shifted to six of them holding the Omnicidal Maniac Jagganoth back from destroying The Multiverse — and one of their number, Incubus, wants to tip that balance again.
- Great Britain's foreign policy from the late 1500s until the 20th century was keeping a balance to ensure that no one got big enough to invade England or challenge its supremacy. The reasons for this was that England had a much better naval tradition than a land-based military, and continental supremacy depended on the latter. As such England always keyed its foreign policy in Europe with the view that it could prevent or hamper the growth of a great power, and/or cultivate allies whose armies could serve, to put it crudely, as Cannon Fodder, facing the bulk of the damage of land and lives relative to England.
- Henry VIII did the opposite (joining the strongest side) to try and grab territory around English Calais (where the Valois and Habsburg lands overlapped). But the minute he launched the Protestant Reformation, albeit inadvertently, he burned that bridge, and made England into the allies of "weaker" Protestant nations, leading them to support the Dutch, albeit only nominally, while secretly undermining Spain. Elizabeth I didn't want England to back any losing horse, or be put in a position where she would have to commit, so she ran her regime much more cautiously, publicly avoiding war with Philip II of Spain, while privately and covertly patronizing English smuggling and piracy in the Caribbean against Spanish colonies. British-Spanish and British-French wars in the later 17th and 18th centuries were over trade, trade posts, and (to a much lesser extent) colonies. And eventually the English fought Protestant Republican Dutch too.
- During The Napoleonic Wars, England ensured a fortress of ships defended it from French invasion, and she relied on using her great financial resources to suborn and subsidize European allies, especially Prussia, Austro-Hungary, and Russia, to break alliances and battle against the French. The largest land battles of the Napoleonic Wars, Borodino and Leipzig, the latter of which saw Napoleon lose at the height of his powers, did not cost a single British life.
- Britain did oppose Russian expansion in The Balkans and Central+Far-Eastern Asia, but only so she could nab The Middle East and India and trading posts in China for herself - Anglo-French Rapprochement (as per the Crimean War) and the Anglo-Japanese Alliance were cornerstones of this.
- Britain didn't oppose German expansion on principle either, they just did it because it was cheaper than opposing French expansion (because France's Empire was bigger and shared more borders with Britain). This later facilitated an uneasy Anglo-Russian rapprochement when France became Russia's ally in the 1890s, allowing Britain to cut down even further on defence costs. Likewise when Prussia went to war, it was predicted (rightly) that the bulk of the battle would be fought on the soil of their continental allies and it was necessary for England's traditional view of attrition that they nurture continental allies to bear the brunt of the enemy's fire.
- Intervention on the side of the Entente in World War I was done to smooth over domestic unrest because Irish Home Rule was about to come into effect and the country was being wracked by massive social unrest instigated by Womens' Rights Activists (who wanted female suffrage) and striking Labour Unions (who wanted an end to child-labour, lethal working conditions, and seventy-hour weeks) - meanwhile, the left wing of the Labour Party was doing its best to channel all of this into Revolution. The 'best' solution - a years-long, cripplingly-expensive War Of Attritionnote - demonstrates the seriousness of Britain's 1914 domestic political crisis.
- Some newly found Soviet conversation logs from around 1990 prove that Margaret Thatcher was actively opposing the reunification of Germany even when the whole east of Europe was already revolting against the Soviets. Only to keep the Balance of Power intact. Confirmed by the diaries of her junior minister Alan Clarke, who was disappointed that she didn't back the reunification he realized was inevitable. Even at that time she was quite obviously not in favour of the reunification, so probably no one is surprised about the discovery.
- Pre-World War I Europe was much like this, except that there were three to six top-tier powers (Britain, Germany, and France at minimum, then Austria-Hungary, Russia, and Italy), with alliances shifting more frequently than you can shake a stick at. On top of that, there were the smaller powers, such as the neutral Low Countries, and the newly-minted and aggressively nationalistic countries of the Balkans (Bulgaria, Serbia, Greece, and Romania topping the list in belligerency and grandiose designs).
- The Cold War was very much about this, although the Superior Firepower and Mnogo Nukes meant that outright war was relatively unlikely. Instead, the US and USSR decided to fight by proxy. There is some variation as both the United States and Soviet Union were so powerful that even if one of them lost a useful ally like China - as per the Sino-Soviet split and Sino-American rapprochement - the balance never shifted firmly in favor of the other side.
- Other countries during the Cold War had become sick of the American and Soviet deadlock and so tried to Take a Third Option. Nations such as India, Yugoslavia and Egypt formed the Non-Aligned movement. While Charles de Gaulle had become skeptical of NATO and a pro-American foreign policy that kept France dependent to the Western bloc, to this end he opened trade relations with the Soviet Union, pulled itself out of NATO and developed nuclear potential and tried to constantly veto England's involvement with Continental affairs, factors which made him highly unpopular both at home and abroad. Ironically when France finally had a socialist President like Mitterand, they started moving away from the Soviet Union and drifted towards liberalization of economy and the Western bloc in the 80s.
- For much of its existence, the USSR also had an internal balance of power: the three-way rivalry between the Army, the Communist Party, and the KGB. Whenever one of these elements threatened to become too powerful, the other two would cooperate to weaken it. As soon as the threat was eliminated, the alliance would dissolve.
- The Constitution of the United States similarly invokes this situation among three branches of the Federal Government (the Congress, the Presidency, and the Supreme Court), the idea being that if the government is busy fighting itself it can't oppress the people. Historically the leading branch has swung back and forth between Congress (embodied by the Speaker of the House) and the Presidency as the A and B, with the Supreme Court staking its claims to power on occasion as the E starting with Marbury v. Madison.
- The Peloponnesian War represents how the equation can go awry. It was very bad to be an E. Both A & B (Sparta and Athens) decided that the situation was a lot more stable if there weren't any Es around, and generally went about destroying them. Also, it was the Cs & Ds (like Corinth) who started and restarted the war between A & B, figuring that the worse off the superpowers were, the better off the medium powers were.
- Except there was one Enormous E - the Persians. While they failed in direct assault, they always had more than enough gold to ensure the balance was maintained. At least two Greek invasions of Asia were forced to stop due to the Persians bribing the invaders' neighbors into a backstab. In the end, a treaty was signed making the Persian king the main power ensuring peace in Greece.
- Ancient Mayan city-states declined in a similar way, as well as poisoning water supplies.
- Ancient Rhodes, a noted Merchant City in the Hellenistic era, survived by its expertise in maintaining the balance between the Successor States, and ensuring that its small but extremely skilled navy was capable of tilting the balance back whenever one warlord became more powerful then the Rhodians liked.
- Renaissance Venice did this as well between Spain and the Ottomans.
- Wolfers was a political scientist who wrote about how a balance of power is impossible to achieve because, even if it is attained (or roughly attained), it's never in A or B's interest to maintain a situation where they are as powerful as their foe, which means that they fight client wars in spheres of influence and get into arms races.
- Arguably Balance of Power is best thought of as a classic strategy to ensure the survival of one faction (as witness Rhodes and Venice above), rather then a way to keep the general peace. In other words the main point is that other people are fighting each other rather then ganging up on you. The exception, of course, is the modern iteration of the strategy, Mutually Assured Destruction: where if A and B fight, everyone loses.
- Before the Second World War there was Great Britain and France, the expanding Axis Powers, and the Glorious Soviet Union, each with an ideology that was unacceptable to the other two. Both the Glorious Soviets and the British knew that, if they went to war with Germany, afterward they would be weakened and the other would exploit it and attack immediately. In the end the Glorious Soviet Union made a pact with Hitler to divide Poland and force Britain to go to war with the Axis Powers.
- During the Soviet Invasion of Afghanistan, the mujhadeeen were supplied with weapons and training by both Western and Islamic countries... And China, in spite of it being a Communist power like the Soviets. The reason why can be traced back to the aforementioned Sino-Soviet Split, since China had no interest of being encircled by the USSR if Afghanistan became another satellite state like other countries in the Soviet bloc and it didn't help the pro-Soviet Afghan government supported Vietnam, which was China's enemy at the time.