According to a good deal of Speculative Fiction set in The Future™, it is the natural order of things that all governments will merge together to create a central authority to govern the entire species. It's not necessarily the human species, however.
Sapient aliens also almost always have a single government to whom every law-abiding sophont in their race answers. Any conflict between members of the same species will be called a civil war. Especially true if The Verse of the show contains boatloads of sapient species.
The examples can cover a range of extremes: the government is benevolent, efficient, enlightened and out for your well-being; justdownright evil; or plain realistic, or anything in between.
It may be true that in order to expand to the stars, a species would have to pull together as a team and overcome the tremendous challenges involved. However, this just seems like laziness on the part of the writers, as tracking more than one government per alien seems like too much work.
Every species in the increasingly crowded galaxy will also have a single unified culture. It can be detailed, as for an alien in the main cast, or it can be a one-note quirk if the creature in question hails from this week's Planet of Hats. Either way, it is rare for any species to have more than one language, artistic tradition, religion, or culinary style.
This trope is not necessarily unjustified. There are a number of conceivable differences in the way an alien race's history played out versus our own that could result in their world being more unified than ours. For example, if their starter population and/or landmass was smaller, or if one tribe conquered the others.
If the species in question is humanity, there may be more diversity involved, if only because the writers don't need to invent it all. The aliens may also look the same. See Ditto Aliens. See also Planetville.
Note: If you happen to be in a Christian "End Times" story, and a single government controls the planet, watch out for the dude with the goatee. Alternately, watch out for the guy standing BEHIND the dude with the goatee. If the "villains" are seeking a One World Order to remove the political divisions that enable international war, they may be Well Intentioned Extremists. If the villains go even further than that, it could be an Assimilation Plot.
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In One Piece, the entire world is ruled by the aptly named World Government. In the past, there were other countries (at least 20) but they banded together to defeat the old world power. Nowadays there is a civil war led by the Revolutionary known as Dragon.
There are still many minor governments, but the World Government is working hard to incorporate them (sometimes peacefully sometimes... not), or obliterate them and send their populations to slave works. They are that kind of people.
The latter half of Gundam X focuses on the remnants of the old Earth Federation trying to reclaim their old influence... by forcibly conquering Europe, Asia, and Africa. By the end of the series, though, they're still having a hard time with North America (they really didn't expect the generally lawless and fractured city-states and Vultures to band together against them) and the remaining space colonies are not pleased with the Federation's revival.
In Gundam Wing, we get to see this in action as the Romefeller Foundation uses their overwhelming military power to conquer the planet, forming the World Nation. Then they make Relena their figurehead leader and she pulls Reassignment Backfire by turning the World Nation benevolent. At the end of the series, the World Nation surrenders to the colony rebel army White Fang, and between then and The Movie it becomes the Earth Sphere Unified Nation, which despite the name seems to be a more benevolent Federation.
In the Universal Century Gundam shows, the Earth Federation had long established control over the entire planet. On the other hand, it's presented (especially further down the line) as an elitist, bureaucratic mess rife with corruption. Their reach beyond the planet is also shown to be shaky at best, with many of the colonies not exactly eager to be under EF rule. And it's strongly hinted that their grip on Earth itself progressively becomes less stable.
It was also the same case in Gundam AGE, except their enemies are Martian colonists with a grudge for the corrupt Earth government.
In Monster, many organizations hope that Johan Liebert will lead them to this. Johan Liebert doesn't care about any of that as he shows all of them that Evil Is Not a Toy.
Code Geass has the Holy Britannian Empire become this briefly in the end after the Final Battle, conquering the fledgling United Federation of Nations. After Lelouch dies, Britannia gives up those recently-conquered territories and begins to coexist peacefully with the rest of the world.
In one Justice League of America story, it's explained that the reason so much cosmic weirdness gets drawn to Earth and not other inhabited worlds is that Earth is unique in the universe for having a multitude of different races and cultures. Go figure.
Similiarly, Green Lantern/Sinestro Corps Secret Files claims that Earth is "the most diverse and emotionally rich planet in the universe, boasting more differing cultures and languages than most galaxies".
Some Jack Chick tracts are set in a world ruled by a single (and malevolent) government, as foretold according to some interpretations of Christian end times prophesies.
One Nation Earth is in control of all the earth throughout all the movies in the Apocalypse film series so far, and has been shown to be rather oppressive to both Christians and those who have not chosen a side.
The Starship Troopers universe had one government controlling Earth and all colonies. There was a massive war between China and Russia/Europe/America and after 90 years a wave of revolts in Europe overthrow the current governments and formed the United Citizens' Federation, then the Americas did the same. Finally they decided to go to war with China (and anybody who was left) to create the peaceful loving government we know. Do you want to know more?
Thousand Shinji: "Today there are no more nations, there is only humanity."
In David Wingrove's Chung Kuo, the entire world is ruled by the Seven and simply called the City, or Chung Kuo.
But... at the same time the trope is somewhat averted. Several alien species hail from a number of planets - Duros, Twi'leks, Zabraks, and, yes, humans, all come from any number of worlds rather than just One World Order. Even the Mandalorians (more of a loose cultural affiliation rather than a species) now come in more than one variety, each wildly different than the other, thanks to Star Wars: The Clone Wars. It's also worth noting that the galaxy is, itself, often depicted as a multispecies coalition rather than as single-race empires.
Starfighters of Adumar is about, among other things, a planet that had been human-colonized and left isolated being discovered by the New Republic and the Empire. The planet, Adumar, was a nonunified mass of countries, many at war with each other, making trying to get the world to affiliate with one or the other complicated. Negotiations were with the leader of the largest country with the greatest number of allies. He was trying to unite the planet under him; other countries weren't having that, and there was a battle. The bottom line has a world government formed from representatives of each country, rather than that one guy.
In the Left Behind series by Tim LaHaye and Jerry Jenkins, The Antichrist becomes leader of the UN and creates the Global Community, declaring a single world government, currency, and religion. No one objects, and it's not clear if this is supposed to be because of his Mind Control abilities. Its successor, the universal state created by God after the Second Coming, also qualifies as a (supposedly) more benign example.
Ira Levin's This Perfect Day has the entire world unified under the control of one gigantic supercomputer, although the backstory shows that political and cultural unification predates the building of UNICOMP by a generation or two, while each continent had its own computer before that (EUROCOMP, USACOMP, et cetera). This political unification is one of the few things about his society that doesn't annoy the hero so much that he decides to blow up the computer.
This is one of the main points of the paradise-like Third Earth of DJ MacHale's Pendragon.
In Peter F Hamilton's The Night's Dawn Trilogy, Earth deliberately creates colonies of this sort by a process of "ethnic streaming", to avoid giving people obvious differences to fight over. This is realised after the first, multi-ethnic extra-solar colonies descend into anarchy. Earth itself has a unified government, GovCentral.
In Dan Simmon's Hyperion Cantos books, the Hegemony of Man is a Multiple-World Order, with almost 250 planets under one government, all connected by millions of Farcaster portals.
The United Nations fulfiled this function (in Literature/Rocketship Galileo by Robert A. Heinlein peace is enforced by the guided rockets of the U.N. World Patrol, while The Ganymede Takeover by Philip K. Dick makes reference to the U.N. Army fighting the Alien Invasion) before they became synonymous with corruption, indecision and inefficiency. Of course, that in itself can be a useful trope, as seen in the contemporary Takeshi Kovacs novels by Richard Morgan, where a U.N Protectorate maintains its rule over the Earth colonies by propaganda, military force and subtle corruption.
A particularly cynical version appears in Larry Niven's stories of Svetz the time traveler. The "SecGen" is apparently the absolute monarch of humanity, but the current SecGen (the product of centuries of inbreeding) is a grown man with the mind of a small child. The actual control of the government rests with those who are most successful at bureaucratic infighting and at cajoling the SecGen into approving their decisions.
It is strongly implied that The Church of His Dark Materials wields de facto (if not de jure) power over the whole Earth. At least in Lyra's universe.
Carrera's Legions: The UN became this several centuries prior to current events in the series, and was renamed United Earth after the concept of nations was eliminated through legislative and bureaucratic methods.
In the Childe Cycle, the worlds of Newton, Cassida, the Friendlies, and Exotics are governed by strong planetary governments. Newton and Cassida are ruled by technocrats, the Friendlies are a theocratic republic, and the Exotics are... unique. Though there are constant sectarian violence with the Friendlies, their leadership is powerful enough to keep things in order.
The Tower and the Hive series has humanity united under the Star League. In the Pegasus trilogy, we get to witness the evolution of the United World; while the world is united under one government, that government is composed of layers of international institutions, and the various nation-states still exist and retain sovereignty.
The UHU (United Human Universe) in Maurice Dantec's Cosmos Incorporated although it's vague on how much actual power it has as national governments still exist under it's umbrella.
In The Moon Maid by Edgar Rice Burroughs, Earth is united under "the Anglo-Saxon race," and governed jointly by the United States and the United Kingdom. This is broken in The Moon Men, when the Earth is invaded by the lunar people.
EarthGov is more of a national alliance than the traditional One World Order, but it's the only representative of the entire human race to the other races.
The Centauri and the Minbari are of the more traditional interpretation of a One World Order, each as the sole government of their respective races.
Despite the fact that the humans in Battlestar Galactica come from twelve different planets, there is only a single primary religion among them (although some groups are more extreme or dogmatic in their beliefs than others, and atheism definitely exists in their culture as well). However, in the original series, at least, there are different sects referred to, and a guarantee of religious freedom is part of Colonial law, or at least culture. It's also arguably justified by the fact that their gods seem to exist physically in some form.
At least in the new series, the Twelve Colonies are implied to have been in contact since their founding, making it fairly reasonable that they would have a fairly unified culture. The really surprising thing is that different skin colors and British accents still exist, and yet don't seem to map at all to colony of origin.
Not entirely true; apparently Baltar overcame an Aerilon (Yorkshire) accent so that people wouldn't know where he was from. Still doesn't explain why he has a British accent and everyone else pretty much speaks with a generic American accent.
Also, there are certainly other cultural differences; the people of Gemenon take their faith much more seriously than those of the other colonies, and the people of Sagittaron don't believe in modern medicine.
The Colonies may be united but they haven't been so for many years and they only did it because of the common threat presented by the Cylons. Before unification, it is mentioned the Colonies were very much at each others' throats. Which is why they built Cylon Centurion model robots in the first place. And old hatreds still run deep in whats left of the Fleet. It is occasionally mentioned the ships with mixed populations tend to be the most unruly.
All of that is depicted in the Prequel series Caprica; the Colonies are all independent states, with different forms of government (although since each colony is an entire planet, it still semi-fits this trope). For instance, given talk of a "Prime Minister" and "Commerce Minister," it appears that Caprica itself (later capital of the Twelve Colonies) is a parliamentary republic. Also, it turns out that there wasn't just the one religion: a few people were monotheists.
Other sources such as The Caprican online newsletter explain a bit more of the differences between the Colonies. Leonis was an empire (albeit one in decline) and Virgon is a parliamentary monarchy and both had colonised Tauron for some time. Tauron was a democracy before the civil war but is hinted to be a military government. Aquaria/Aquarion, owing to its tiny population, could afford to have a participatory democracy. What is consistent is that almost every Colony, even the ones that share friendly relations, suffer from prejudice and dislike towards one another. It's explained that if it wasn't for the threat of the Cylons, the Colonies would not have united.
Star Trek is the number one utilizer. The Federation is in fact a government for several species, and it's rare for there to be any diversity in alien culture except in service to the plot. (Benzites do not report a situation to their commanding officer until they have fully analyzed it, for example, preventing a Benzite crewmember from heading off a situation before it can escalate to a dramatic level.) In one episode of Star Trek: The Next Generation, Picard and Beverly even discuss whether or not having One World Order is a prerequisite for Federation membership. (It isn't, technically, but apparently the question has never come up before.)
Deep Space Nine was a little less blatant about this, partly because they stayed in one place so could get a bit more involved with the politics of alien races (particularly the Bajorans, who were shown to have different "provinces" on their planet, as well as at least one terrorist splinter group) and partly because it was Darker and Edgier anyway.
Unfortunate Implications abound: The Federation seems to be unable to truly coexist with any culture without absorbing it, and its rivals - empires of similar size - are shown to be not only culturally but racially homogenous.
The former point is made on Deep Space Nine by Michael Eddington: "You know in some ways you're even worse than the Borg. At least they tell you about their plans for assimilation. You're more insidious. You assimilate people and they don't even know it."
Quark also lampshades the issue in "The Way of the Warrior"...by comparing it to root beer.
Garak: It's vile!
Quark: I know. It's so bubbly and cloying and happy. But you know what's really frightening? If you drink enough of it, you begin to like it.
A few seasons later there's a call back to that statement. When the Dominion invades the station, Quark is all too happy to throw out all the root beer and human food and stock for his new Cardassian customers. However, after a few months, Quark admits that he wants the Federation back on DS9 and that he wants to sell root beer again.
There is also a different explanation; maybe it's not insidious assimilation. Perhaps you just begin to like root beer because it's an acquired taste...just like The Federation. They're the most benevolent guys around, abounding with reasonable authority figures (Section 31 notwithstanding) and all sorts of benefits for their citizens, tangible and intangible, while pretty much anywhere else such niceties are very hard to find. There's nothing wrong with choosing root beer when the alternatives are unpalatable and you don't want to go thirsty.
In Firefly, the Alliance more or less rules all planets inhabited by humans, and has thoroughly put down the secessionist rebellion of the Independent Faction (in which Mal Reynolds served as a Browncoat).
In SeaQuest DSV, United Earth Oceans appears to be this for all intents and purposes, at least until the third season, when the show was renamed to seaQuest 2032. In the ten years between the second and the third seasons, another major power arises, the Macronesian Alliance, starting a Cold War with UEO. This is in an attempt to make the show Darker and Edgier.
Defiance: In the wake of the Pale Wars, the Votan Collective factionalized while most human governments collapsed. In the years since, the major remnants of both have come together to form the Earth Republic, which is nominally one of these. That said, there are groups (such as the titular town) that are independent.
I.C.O.N. (International Confederation of Nations), which has wiped out all religions except for Judaism in Hero.
The "New World Order" conspiracy theory is played both ways in the Dark•Matter campaign setting for d20 Modern (well, unless your GM modifies things) — the conspiracy theorists are right in that the UN intends to unite humanity, and they are right in that black helicopters are used by the UN elite forces. It's the other bits that are mistaken: It is suggested that the UN's leadership would prefer this to be a democratic state, which is one reason why it has taken so long, the UN have solid, sensible reasons for thinking a human unification to be a Good, or at least Necessary, Thing, and they have Christians amongst the top ranks.
The Technocracy in the Mage: The Ascension game from the Old World of Darkness. Literally committed to and highly successful at shaping the beliefs of the entire human race. Due to the consensual nature of reality in the setting, this collective perception of how the world works literally defines even the rules of magic and science. In fact, the only reason science and technology work at all is because the Technocracy has convinced the masses that it is supposed to. New technological innovations are introduced into the consensus at the Technocracy's discretion and they ruthlessly try to stamp out "reality deviants" that threaten their hold over humankind. Obviously, all of this requires them to manipulate everything from the media to governments. Their leading sub-faction is even called "The New World Order". They do cheat and break their own rules of course, employing technology far beyond what they have allowed the general public to believe is possible. Up to and including interstellar space travel.
The Tau Empire in Warhammer 40,000, though as their fluff is expanded, differences between Tau Septs are starting to appear.
This actually makes a measure of sense. The Tau homeworld was contentious and wartorn until the coming of the Ethereals and the firm establishment of the Caste system united them for the Greater Good. Then came a period of glorious victory and expansion. Now, they're butting up against the big boys and having to face against the horrors of alien races. This is the cause of most of their divisions.
The Architects of the Flesh from Feng Shui have set up one of these in 2056, run by the Bureau of Tactical Management (or the Buro in short). The population is kept in line through powerful feng shui, though there are still pockets of resistance around the world. There's also one major area that is immune to the influence of Chi and where technology more advanced than ancient weapons just doesn't work, watched over by the Vikings.
In the setting of Crusader, the world (indeed, the solar system) is ruled by a single government, the WEC. Simply put, the WEC is every corporation in the world, merged into a hypercorporation, ruling the stead of a government.
The truth is naturally more complex than that, but this is a very useful lie.
Once you control 8-9 of the 10 cities, the others will hail you and explain that they "see the writing on the wall" and just join your empire on the spot.
The EDEN empire in the Galaxy Angel games encompasses a lot of diverse planets, but yup, each one has one culture to its name. Parodied (as with all things) in the Galaxy Angel anime, where there are such things as industrial planets, resort planets, etc. owned by one person.
Earth finally uniting as a One World Order is the reason why the Cyrollans extend an invitation for humankind to join the Symbiotry of Peaceful Beings in The Journeyman Project and why a key element in Dr. Elliot Sinclair's plan to prevent the Cyrollans, who he sees as a threat - legitimately so, as the third game reveals - from having an interest in Earth involves disrupting the peace talks that resulted in Earth's unification.
This is the goal of Deus Ex Evil CEO Big Bad. By buying influence with money or blackmailing with a critical vaccine, he can have his choice of appointees in any government agency in the world, and have the legislation drafted to give them authority to declare and maintain martial law. He gradually stages legal coups to make the transfer of authority to a U.N. enforcement agency permanent, consolidating control of all governments.
Mass Effect plays with this a bit — the codex notes that Earth is still controlled by several sovereign nations; however, anything outside the solar system is controlled by the Systems Alliance, a supranational body that controls human space business independent of any individual nation's interest, by necessity: the bickering nations couldn't effectively run an empire of that size.
Mass Effect both uses and subverts this trope. On the one hand, there is a galactic council that oversees issues relating to the entire galaxy. But the in-game literature also talks about how separate, smaller governments still exist. Also, they mention how each other species has as many varied languages, cultures, and religions as humans do.
Even at a species level, truly unified government seems rare: the Turian Hierarchy is fairly centralised, but the Systems Alliance is a multinational organization that provides interstellar defense and diplomatic representation to Earth's actual nation states, the Salarian Union is a semi-feudal collection of independent matrilinear clans, and the Asari Republics barely qualify as a government at all (Their council member is the only permanent asari political office).
Project Sylpheed gives us the Terran Central Government (TCG), which apparently rules the entire Earth and its colonies. It has the Terran Central Armed Forces (TCAF) as its military.
Played straight in the Dead Space series with EarthGov. It's mentioned in background sources that this was the result of several wars, political upheavals and the depletion of natural resources planetside. It's also mentioned, however, that special preference was made to the United States.
In Deadalus aka. Robotica, the Earth is united under the World Silent Security Systems, based on the space station Deadalus.
In Futurama Earth is under one government based in Washington D.C., implying that the U.S. has taking over everything. Its flag, "Old Freebie" is just the Stars and Stripes with a globe in place of the stars. Earth, in turn, is part of the Democratic Order of Planets (DOOP), analogous to the United Nations (or to The Federation, which is how the Star Trek-obsessed Fry understands it).
Moreover, all bureaucrats — apparently all of them, in all organizations, commercial, governmental or otherwise, large enough to require any bureaucrats — are members of a single Central Bureaucracy.
Teen Titans: Starfire's family are the rulers of all of Tamaran.
In Danny Phantom, this is what used to be for the Ghost Zone when the evil dictator Pariah Dark ruled it with an iron fist. Naturally, the citizens weren't happy and rebelled. He tried to get his kingdom back AND take over Earth, but he had Big Damn Heroes on the opposite end.
In Time Squad, Larry and Buck explain to Otto that by the year One Million, Earth had eventually merged all its countries into one big "super-nation."
Subversions And Aversions
In the Star WarsExpanded Universe, species that don't have much to do with the greater galaxy are quite capable of maintaining several different cultures, factions, sects, teams, and fan clubs.
A good aversion of Scifi Writers Have No Sense Of Scale. Since a vast majority of star systems in the galaxy can (and do) support sentient life, there are simply far too many races and planets for all of them to be homogenized under one banner. Even The Empire at it's height controlled maybe 60-65% of the galaxy and had nowhere near enough soldiers or starships to make their presence known outside of space-faring systems, with many "mini-Empires" and planets that enjoyed de facto autonomy. Chances are good that hundreds, maybe thousands, of star systems within the Empire's borders watched it come and go without ever having known it was there.
Anime & Manga
Averted, subverted and occasionally played straight in the Humongous Mecha manga series The Five Star Stories, where out of the half-dozen or so habitable planets orbiting the titular stars, only one is unified under a single government and wars between the various countries on the other planets are extremely common. As national identity is a major theme in the series, the aforementioned planetary empires attempts to unite the others through military conquest later in the series... doesn't turn out so well. On the other hand, in the series' backstory, we find that the entire galaxy and then some was united in a mystical "Super Empire" in the distant past.
The Gundam series in general are a subversion of this trope; when colonies are established in space, they inevitably try to become independent from Earth resulting in Space Wars.
The Universal Century timeline comes close, in that the Earth Federation rules over all of Earth and generally claims sovereignty over the colonies, but some colonies are not overly happy about this. Even the UC colonies aren't a unified bunch. Side 3 makes up the heart of Zeon (considered semi-autonomous after the One Year War, albeit with a puppet government controlled by the Federation in reality), while Side 6 declares political neutrality in the One Year War, Side 4 briefly becomes the Cosmo Babylonia aristocracy, while Side 2 eventually becomes the Zanscare Empire. Then there's the Jupiter Sphere, which is technically considered part of the Earth Federation (by the EF, anyway), but they're so far away that Earth can't really enforce anything on them, so they consider themselves independant. That's not even mentioning the whole situation with Axis. Needless to say, the UC timeline totally destroys this trope.
Gundam SEED frequently refers to the Earth as though it were one political entity, but this isn't the case. It is in fact divided into seven or eight supranational blocs, as well as the Orb Union, a small but powerful south Pacific island country. Most of them are united in a military alliance under the Atlantic Federation, which is hostile to the space nation of ZAFT. However, a couple of nations on Earth support ZAFT, most notably the Oceania Union (Australia + New Zealand), which lends ZAFT the use of a large naval base at Carpenteria, and a few others remain stubbornly neutral in the whole affair, including Orb.
Gundam Seed Delta Astray establishes the existence of the Mars colonies as well, a recently-established group of space colonies (Mars itself not being terraformed). They're considered a separate nation. There was also another colony that converted itself into a giant spaceship and headed for Jupiter (notably without the consent of whichever nation owned it), because its citizens saw the constant conflict the Earth Sphere was getting into and basically said "Screw This, I'm Outta Here!!"
Averted in G Gundam, the United Colonies Federation is merely more like the present United Nations, and the nations themselves are independent on each other. It is just that the country wins the Gundam fight will be for four years the leading nation in the Earth Sphere.
Legend of Galactic Heroes subverts this in the long run. Planets by and large are run by only a single government, usually under either Empire or Alliance. But the sheer expanse of space (and not to mention human nature) means that humanity doesn't stay united for long. T
Inversion of Enforced Trope in An Entry With A Bang!: The writers have mostly agreed that, despite Clancy-Earth presenting a united front in their relations with the Battletech entities, the countries on C-Earth proper will not unite into a super-entity in its purest state of a truly singular government, but exactly what the CSN's political structure is to be instead is a discussion that has gotten inflammatory at times.
Star Trek: Into Darkness subverts this. While the Earth's united, there remains cultural and national diversity, with at least some present-day countries apparently surviving into the 2250s in some form. The Union Jack is still shown flying in London, suggesting that the UK made it as well. While in a bar scene involving Kirk, what looks like an American flag appears to be in the background. However, this may be in line with some TNG material which references a starship being built in the Soviet Union; old Earth still countries exist, but are subsumed into a federal United Earth government.
The Left Hand of Darkness, in which Gethen has several different countries. The protagonist eventually visits the country of Orgota, to find that its government and customs are vastly different from Karhide, and even mentions that he's not as familiar with the native language.
Similarly, in The Dispossessed, Urras is divided into several countries, including (at minimum) the liberal democratic capitalist A-Io and the "socialist" totalitarian state Thu, which are fighting a proxy war in unstable Benbilli. If this sounds like the Cold War...well...it should. Urras, it should be noted, is a double planet, with its (relatively) barren partner Anarres having been settled by "Odonian" anarcho-syndicalists who, as such, have no state. Although LeGuin is herself a noted anarcho-syndicalist, Anarres averts Mary Suetopia by having a legion of problems, including the development of entrenched bureaucracy among the "syndics."
In Out of the Dark, the Shongairi are confused that humanity managed to get to our current level of advancement without becoming this.
Subverted with the Dorsai in the Childe Cycle. Though officially they have a planetary government, the Dorsai are fiercely independent folks. As a result, the world government has no real power in comparison to the other worlds.
Played with Ceta - the planet has several nation-states. However, thanks to economic and social engineering, they're all under the de facto rule of William of Ceta.
Averted with Earth (and New Earth!) in the Cycle - there's still plenty of various national governments.
Lampshaded in Alien Nation when Sykes is surprised his Tenctonese lady friend follows a more "Eastern" religion, then admits it's stupid to think an entire race of people would only follow one belief system.
The Goa'uld are ruled by a group called the System Lords; true to their name, their government is generally very feudal, with Goa'uld serving different leaders, trying to empower themselves, and at war most of the time (using expendable human slaves).
Some human planets are also divided, including the unnamed planet in "New Ground", Euronda in "The Other Side", and Jonas Quinn's homeworld. And Earth, of course.
Even the Asgard (who are all clones) mention having political strife (although we never actually see much of it).
This trope is justified in a few cases where we see a free (but undeveloped) planet; the entire civilisation is generally within a few days' walk of the stargate so is much smaller than a lot of countries on Earth.
Interestingly, while later incarnations of Star Trek are definitely associated with this trope, the Original Series frequently averted. Many worlds had two conflicting cultures, which were always metaphors for an Aesop on either racism, classism, or The Cold War.
Also, the Vulcans, in a way: they tried to unify politically and culturally their race, but in the end that resulted in creating the Romulan Star Empire in contrast with Vulcan proper.
The backstory universe of BattleTech has the One World Order forming and collapsing no less than 4 times! First Earth became a one-world order who sent out space colonies. Eventually the colonies rebelled into several bickering nations. Finally a force of personality united the bickering 5 major nations into a united One-Galaxy Empire. This collapsed after a Usurper killed the leader and his family and the five nations each claimed the throne. The Army of the now gone One-World Government fled and set up a new one world government of its own (the Clans). After 300 year of fighting, these clans returned. After an initial thwarting, the One-world-Order leader of the Clans was dissolved. In eventual response to the invasion, the 5 governments recreated the original one-world government again as a united force to stop the invaders. after the invaders stopped, the government, its mission accomplished, was dissolved. At which point an army of religious fanatics attempted to take on the whole galaxy to recreate another one-world government in their own image. The point seems to be that One World Orders aren't viable...up until you realize that if a sustainable version were to be created, the game would end.
...or just tear themselves apart anyway, 'cause that's how we roll. After all, Real Life governments of all sizes have a habit of doing this once there's nobody left to fight, too. Battletech always was one of the more intensely political fantasy/sci-fi universes.
Traveller: Played with. The Third Imperium is the dominant power. However the Imperium has thousands of subsidiary governments, sometimes several on the same world, as well as governments outside the Imperium. Planet Terra itself is usually under one government.
The final villains ofAce Combat Zero: The Belkan War seek to bring about peace and correct the non-OWOness of humanity by eliminating the political entities, ergo governments and borders, that lead to war.
Galactic Civilizations II appears to follow this trope at first, with civilizations named after their race and all the usual trappings. But in many situations it's highlighted that none of these space-faring civilizations speak for ALL their species, just the ones that got into a big ol' pile and started starfaring together. For example: If any one planet has a monumental population boom, the news will go out of its way to state that the 2 billion new faces couldn't possibly have been born in less than a year, and that much of it is from same-race foreign immigrants applying for citizenship.
There are also various political parties in the game. You choose a specific political party at the beginning of the game that grants bonuses to certain statistics. If you decide to change your government from an empire (the default) to a democracy then you must keep up your popularity or have a new party take control and make you lose your party bonuses.
Most of the alien races from the Star Control games are examples of the trope, but there are a few exceptions:
The Yehat empire consists of several warrior clans that often fight for supremacy. In Star Control II: The Ur-Quan Masters, one can convince a group of Yehat dissidents who despise being Battle Thralls to start a new civil war.
The history of the Thraddash consists of several civil wars waged between factions of their Proud Warrior Race Guy culture that popped up every few hundred years. By the time of Star Control II, the Thraddash were up to Culture 19, and the player can end up inspiring Culture 20 if they beat enough Thraddash ships.
In fact, the plot of The Ur-Quan Masters involves a conflict between two factions of the Ur-Quan race: The Kzer-Za (who want to subjugate all other sentient races in the galaxy) and the Kohr-Ah (who want to kill all other sentient races in the galaxy).
Also averted in Homeworld, at least with the Kharaki/Hiigarans. While the species itself is unified, it's mentioned there are various, distinct clans and houses that serve as countries onto themselves.
More or less the goal in Civilization games. The conquest victory would be an evil example, the diplomatic victory a benign case (although the U.N. does appoint you ruler over everything, including anyone still voting against you, so it can still overlap with the sinister examples). The cultural victory doesn't really imply an abolishment of nations, but more turning earth into a Planet of Hats where the entire culture is like that of your country, so it comes close. The science victory might imply the formation of The Federation when you travel to another star, but it seems more like telling the world "Screw you guys, I'm going to Alpha Centauri".
While the United Nations in Halo, or rather the UNSC serves as a unified front against the Covenant, it's mentioned that it's more or less a projection of the modern-day UN rather than a world government. Among others, it's stated that individual countries, organizations and cultures are still very much alive.
No one ever refers to the three-sided Strand War in Escape Velocity Override as a civil war, despite the fact all three Strands belong to the same species. On the other side of the coin, the United Earth (which only came to be through Alien Invasion in the first place, so nothing natural about it) doesn't make any real claims to represent humanity as a whole.
In the X-Universe series, most of the aliens are united under their own racial banner, but on the other hand, the Split Dynasty is split up into dozens of bickering clans who fight for the right to rule, with military coups being fairly common. Humanity is the most fractured, with two powerful factions that hate each others guts - the Argon Federation, a former Lost Colony which controls almost all human territory in the X-Universe gate system, and the highly advanced Earth State, who control the entirety of the Sol system and have fingers reaching into their otherLost Colony, the Free State Of Solara. Minor factions like the Hatikvah Free League are also predominately human.
Parodied in South Park, where it is revealed that in the rest of the Universe, each species has its own planet; Earth was created to be a bizarre mix of all different kinds of things (gazelles, lions, Jews, Arabs, etc.) to form the basis of a TV show.
The entire premise of Transformers is that there are two distinct and warring factions of the same alien race. The overall culture within each faction is largely monolithic, however (Autobots bland and friendly, Decepticons backstabby), and very few characters are presented as neutral or independent. Occasionally, we had characters with unusual or seemingly inappropriate personalities who were nonetheless distinguished by their alliance. Later examples present more complex cultures, especially Beast Wars
There was also Sideways in Transformers Armada, who played first as an Autobot, then a Decepticon. It turned out he was actually an agent of Unicron.