One-Federation Limit

In most fiction there is only one guy named Steve to avoid confusion. Similar to that, each state type seems to be unique in some works of fiction. There is only one federation, one republic, etc.

Sometimes an exception is made in the case of empires to allow more bad guys.

This Trope sometimes occurs when there are only very few countries covering the entire Planet.

Definitely not Truth in Television.

Anime and Manga

 * In Code Geass the world is divided into three main superpowers; the Euro Universe, the Holy Empire of Britannia and the Chinese Federation. There used to be a Middle-Eastern Federation, but it was conquered by Britannia in season one.
 * Averted in Gundam Seed and Destiny. The two dominating superstates of the Earth Alliance are the Atlantic Federation and the Eurasian Federation. The Republic of East Asia is a lesser partner and the United States of South America was invaded and forced to fight against ZAFT.
 * ZAFT is also an alliance, just like the rival Earth Alliance; the name is an acronym. While little attention is paid to that fact within the show itself, the twelve colony clusters are akin to nations within ZAFT. Orb and the other other independent nation of any note (a unified Scandinavia) are both kingdoms.
 * Both subverted and played straight in Mobile Suit Gundam 00: the Union of Solar Energy and Free Nations represents North America while the Advanced European Union represents Europe, but the latter is always referred to by its initials (AEU).

Film

 * Star Wars has only one centralized government in each movie trilogy (The Republic and The Empire) fighting against one group of separatists/rebels (The Confederation and The Alliance).
 * The Expanded Universe has The Empire and The New Republic fighting each other and later brings in more Empires, as well as a Hegemony, a Dominion, an Assemblage, an Aristocracy, several Imperiums, a Confederacy, a Consortium, a Sovereignty, a Union, an Authority, an Ascendancy...
 * Averted in Star Wars Legacy where the evil Sith-ruled Empire is fought by The Remnant of the Galactic Alliance and another Empire, the benevolent Fel-Empire, which is itself arguably The Remnant of the Empire proper.

Live Action TV

 * Babylon 5 has the Earth Alliance, the Minbari Federation, the Centauri Republic (which is actually a monarchy like the late Roman republic), the Narn Regime and the Vorlon Empire. Some races (like the Dilgar, Shadows, and Drakh) have no stated governmental body, while the others have ones only stated offhand or in the background material (Drazi Freehold, Brakiri Syndicracy, Abbai Matriarchate, Grome Autocracy, etc)
 * And all those miscellaneous governments could conveniently be lumped into the League of Unaligned Worlds.
 * Star Trek, which gave us the Federation, uses the "more empires for bad guys" exception. The Romulans, Klingons, Kelvans ("By Any Other Name") and one planet in star system 892 ("Bread and Circuses") had empires, and that's just from Star Trek the Original Series. The Terran Empire (instead of the United Federation of Planets) of the Mirror Universe doesn't really count because it's in an Alternate Universe.
 * Between all the series and the Star Trek Novel Verse, there are a few duplicates, but also a lot of variety. Here goes: United Federation of Planets, United Planets of Tellar, United Rigel Colonies, United Earth, First Federation, Klingon Empire, Andorian Empire, Danteri Empire, Romulan Star Empire, Cardassian Union, Deltan Union, Breen Confederacy, Confederacy of Vulcan, Regnancy of the Carnelian Throne, Gorn Hegemony, Tholian Assembly, Tzenkethi Coalition, Ferengi Alliance, Nyberrite Alliance, Metron Consortium, Sheliak Corporate, Talarian Republic, People's Republic of Coridan, Republic of Bajor, Magisterial Cheka Kingdom, Plutocracy of Ardana, Ubarrak Primacy, Devore Imperium, Krenim Imperium, Karemma Foundation, Kazon Collective, Borg Collective, Vidiian Sodality, B'omar Sovereignty, Hierarchial Order of Voth, Haakonian Order, Hermat Directorate, New Thallonian Protectorate, the Dominion, the Hierarchy.
 * The Star Trek Novel Verse has also brought us the Typhon Pact, a coalition of the "main" Romulan Empire, the Gorn, the Tholians, the Breen, the Tzenkethi, and the Kinshaya. They banded together for mutual protection, just like the Federation, making them a different kind of adversary than the UFP usually faces.
 * The Romulans actually mixed it up slightly, adding a superfluous adjective to be the Romulan Star Empire.
 * The regular Romulan Empire, without the "Star," is probably what they call the planetary government of Romulus proper.
 * Actually, in The Original Series, Kirk and co. encountered "The First Federation", and it appeared in several star charts in The Next Generation and a drink that originated from it (tranya) was stocked in Quark's bar. However, it was never referenced by name again.
 * Actually actually, at the time the First Federation is mentioned, the writers had not come up with the United Federation of Planets yet. Kirk calls the Enterprise a "United Earth ship", implying the name of his government.
 * Actually actually actually, they worked for something called the United Earth Space Probe Agency. Writers have been doing somersaults trying to explain the discrepancy.
 * Early on, the Cardassian Union is more often referred to as the Cardassian Empire, and they probably made the change because there are already enough Empires to go around. Retcon though it may be, I think it actually adds a touch of realism since such powers are often known by more than one name.
 * The latest developments in the Stargate Verse put this trope into play in the Milky Way. We have the Tau'ri (Earth military forces under the UN Security Council, spearheaded by the United States), the Lucian Alliance, and the Free Jaffa Nation. The Goa'uld Empire would fit the list if it still existed.

Tabletop Games

 * Mechwarrior does this a lot. The Federation's name even keeps changing as it merges with other governments (Federated Commonwealth, Federated Suns, etc.).
 * First of all, the universe is BattleTech, and the Federated Suns has only merged once, with the Lyran Commonwealth to from the Federated Commonwealth, and then broke away and reverted back to Federated Suns (permanently) a few decades later.
 * Regardless, the setting does go to rather extreme lengths to avoid having any two powers with any crossover names. Over time they've missed a few -- the Outworlds Alliance and Lyran Alliance, the Free Worlds League, Hanseatic League and Star League, Rim Worlds Republic and Free Rasalhague Republic, and the Marian Hegemony and Terran Hegemony, for example, though half of these examples didn't exist contemporarily - but otherwise it seems quite implausible. The five major states (Lyran Commonwealth/Alliance, Draconis Combine, Federated Suns, Capellan Confederation, and Free Worlds League) avoid any similarity in naming convention, and then they start naming states 'Magistracy', 'Concordat', or 'Protectorate' to avoid doubling up. Curiously, there has never been an empire.
 * There was one major canonical self-proclaimed emperor in the setting's history -- Stefan Amaris the Usurper, whose treachery started a war that killed 100 million people and led to the end of the Star League. After that wonderfulness, calling yourself "Emperor" in that setting would probably be equivalent to calling yourself "Führer" in postwar Europe.
 * With enough expansions, Twilight Imperium can have an Empire, Barony, Federation, Emirates, Universities, Mindnet, Kingdom, Coalition, Collective, Tribes, Clan, and Brotherhood - although not all of these will be in play in single game.
 * GURPS gives advice on how to use this trope in its 4th edition Space supplement, and provides a handy list of synonyms for the types of government it discusses: Anarchy (Anarchate, Free State, Frontier Zone, Libertarian Republic, Post-Polity, Unorganized Territory, Wild Space), Alliance (Axis, Bloc, Coalition, Community, Commonwealth, League, Pact, Sphere), Federation (Concordium, Confederation, Regime, Union, Unity), Corporate State (Cartel, Combine, Conglomerate, Consortium, Hansa, Keiretsu, Partnership), and Empire (Dominion, Hegemony, Imperium, Kingdom, Monarchy, Principiate, Realm, Reich).
 * The original "Known World" map of D&D's Mystara setting featured one empire, one grand duchy, one republic, one syndicracy, etc. It did include a number of federations, but each one used a different designation for its member regions (principalities, emirates, freeholds, jarldoms, etc).
 * Averted with Star Fleet Battles. Plenty of empires (Klingon, Romulan, Lyran), and more than one federation: both the United Federation of Planets and the Gorn Confederation (which is close enough).

Video Games

 * Mass Effect. The main factions are the Asari Republics, the Systems Alliance, the Turian Hierarchy, the Batarian Hegemony, the Vol Protectorate, the Salarian Union and the Illuminated Primacy. On closer examination, this is likely averted because of the turian foreign policy: There are stated to be more 'client races' besides the volus. So, more than one Protectorate.
 * From what we know so far, Final Fantasy XI only has one Republic (Bastok), one Kingdom (San d'Oria), one Federation (Windurst), and one Duchy (Jeuno). There are other Empires than Aht Urhgan, but it's the only one players can get to.
 * Eve Online has the Gallente Federation, Minmatar Republic, Caldari State, Amarr Empire, Khanid Kingdom, and Ammatar Mandate.
 * Minor factions with designs of being nation-states include the Intaki Syndicate, the Thukker Tribe, and Sansha's Nation.
 * The players themselves keep to this trope. When some players decided to roleplay as Intaki separatists, they named their alliance the Intaki Union.
 * Partially averted with the Jovians. The official name of the Jovian nation, according to the map, is the Jovian Empire. However, the Jovians are isolationist, and they don't feature much in politics.
 * The World Building web game Nation States averted this at the beginning, by giving you a list of about twenty possible state types to choose from. Once you reached a high enough level, though, you could make up your own. Unsurprisingly, aiming to be as unique as possible was a popular consideration.
 * The X-Universe plays this trope dead straight, not even using the empire exception. Argon Federation, Teladi Space Company, Boron Kingdom, Split Dynasty, Paranid Empire, Free State of Aldrin, Xenon Network, Kha'ak Hive.
 * The only real question mark is the Terran government, though it is believed to be democratic (possibly an evolution of the United Nations a la Halo).
 * The X-Encyclopedia adds the Hatikvah Free League.
 * Galactic Civilizations: the Terran Alliance, Torian Confederacy, Korath Clan, Krynn Consulate, Iconian Refuge, Yor Collective, Drath Legion, Altarian Republic, and Korx Consortium are the only races with those titles. There are, however, three empires -- Thalan, Drengin and Arcean -- but even on the Galciv website only the Thalans are listed under that title, with the others simply being referred to as "the Arceans" and "the Drengin".

Web Original

 * Defied in Reds!. In the post-WW 2 world, the three superpowers are the Franco-British Union, the Union of American Socialist Republics, and the Union of Soviet Socialist Republics. And that's just the three top dogs.

Western Animation

 * Avatar: The Last Airbender has had only four countries: The Fire Nation, the Earth Kingdom, the Water Tribes and the Air Nomads. The last one was almost completely annihilated and in the present basically nonexistent.
 * Technically, there are more than four. Both Water Tribe countries are independent from each other.
 * Well, the Northern Water Tribe and Southern Water Tribe each refer to the other as their "sister tribe in the South/North", so it could be argued that the separate governments are out of geographical necessity rather than legal standing. Also, though there are significant cultural differences, the two tribes are still far more similar to each other than any of the other nations compare.
 * Don't forget the Foggy Swamp water benders, a Lost Tribe of sorts who are specifically mentioned to still be "kin" to the rest of the water tribes (much to the rest of the tribes' chagrin).
 * The Southern Water Tribe is on the brink of extinction (at least at the start of the series), it's possible there was more political cohesion before the war. The Foggy Swamp Tribe seems to be legally part of the Earth Kingdom, regardless of ancestry (the other water tribes don't even know it exists).

Real Life

 * The five permanent members of the United Nations Security Council are the United States of America, the People's Republic of China, the French Republic, the United Kingdom of Great Britain and Northern Ireland and the Russian Federation.