Ah, Earth. Full of many nations, territories, countries and governments. And yet when alien homeworlds are visited, we only get to see one government.
This is an Omnipresent Trope in Science Fiction where inhabited planets not named Earth are shown to have only one government. The reasons range from someone succeeding in taking over the world to being a mere Planet of Hats to the fact that politics limited to one world are unimportant to stories with interplanetary settings, or because Sci-Fi Writers Have No Sense of Scale and think that the planet would be akin to a town or city instead of a large sphere that can hold hundreds of countries and billions of cities and towns.
This trope can be justified in a couple of ways. If the planet was recently colonized, there may not have been time for it to develop more than one government. The entire population could be a few thousand to a few million people living in and around the first colonization site. On the other side of things, on a homeworld or a long-colonized world, extending power over a planet is much easier than extending it into space. The one-world government can easily put down unrest on the next continent, but subduing another planet in the same system requires several orders of magnitude more effort, by any known or likely means.
- In Transformers Cybertron Gigantion and Velocitron are like this. The politics of Gigantion are not really looked at, but there is only a single city on the entire planet, presumably under one form of government. Velocitron is governed solely by who is the fastest racer. The politics of this position is not essential to the plot, so it was not looked at.
- After the transition to the much more decentralized New United Nations in the Macross-verse, NUNS-affiliated worlds such as Eden and Ragna now play this trope straight by the time of Macross Delta. The independent world of Windermere is also an example.
- Black Moon Chronicles: Zigzagged Trope. After humanity settles on a new world after the forces of evil have destroyed the old one, Methraton tells the human nations that they have to pick one emperor from among their kings who will rule over the entire world, as he won't allow any more pointless warring between them. They select Wismerhill when he is the only monarch to refuse the throne. However, the other kings seem to retain a degree of autonomy (and their titles), given the feudal setting.
- Discussed and deconstructed in Rom vs. Transformers: Shining Armor; the member species of the Solstar Order all underwent extreme globalization before achieving space flight... making them totally unprepared when they encounter other species that haven't gone through this. The Space Knights find the idea that Transformers still have civil wars and multiple, opposing governments after reaching space to be utterly bizarre.
- In Man of Steel, the whole planet of Krypton is governed by a high council. This isn't explained in depth, though.
- Chris Moriarty's Spin Control series draws a specific contrast here. Earth's offworld colonies all have unified world governments under United Nations jurisdiction, but Earth's nation-states still exist and provide an unexpected wrinkle to any negotiations with the homeworld.
- This is nearly always true in the Star Wars Expanded Universe. One of the few exceptions is the planet Adumar in X-Wing: Starfighters of Adumar, which contains several competing alliances of nation-states. The New Republic and Empire start out negotiating with the most powerful one without fully understanding this, leading to problems. Another occurs in a young adult novel with Obi-Wan Kenobi as a Padawan, when he goes on a mission to a planet in the midst of centuries-old civil war. They can't even agree on the planet's name, with the Melida and Daan factions both naming it after themselves, so the Republic calls it Melida/Daan.
- Most of the nations, planets and Space Stations in the Vorkosigan Saga are this. The few exceptions are the Cetagandan Empire and Barrayaran Empires, which are nations made up of multiple planets, and Earth, which is still split up into a gillion countries like today.
- As usual, Honor Harrington never fails to provide examples of all tropes sci-fi, both...
- Played straight:
- The Protectorate of Grayson, a Cult Colony established by a bunch of Space Amish which gets rather abruptly drawn into galactic affairs due to being smack in the middle of an interstellar cold war. They grow teeth very rapidly.
- The Kingdom of Torch, a planet of liberated genetic slaves.
- Mesa, the planet ruled by a corporation... allegedly.
- And averted:
- The Star Kingdom of Manticore starts out as a single-system (but three-planet) star nation which is punching well above its weight class thanks to the Manticoran Wormhole Junction. Later events turn them into the Star Empire of Manticore. This was not Manticore's idea.
- The People's Republic of Haven, at its height, is stated to have over three hundred star systems under its umbrella, most by forced conquest. One Meaningful Rename and dramatic governmental reorganisation later, it sheds over half of those, the rest remaining voluntarily and by their own request.
- The Solarian League includes an almost uncountable number of star systems and is described, only partially ironically, as "the heir to all mankind's greatness". It's also so bogged down by corruption and bureaucratic red tape that it's essentially ungovernable, and by the time of the main story is falling apart at the seams.
- Played straight:
- This is actually the law for colonies in The Genesis Fleet, where colony permits are only given out to a single group per planet in order to avoid conflict. This is why everyone shocked when Scatha brazenly establishes a colony on the already-settled planet Glenlyon. This just serves to indicate that there's no one to enforce the rules anymore, after the invention of the jump drive and the second wave of expansion, as Old Earth is no longer interested in being the "big brother", and neither are the old colonies. In fact, Earth is actually mothballing and selling off its Space Navy. The trope is definitely averted in the case of Earth, which still has the old nation-states, and Mars, which is largely run by gangs. By the end of Vanguard, the Glenlyon colonists manage to retake their world, kicking Scathans off the planet.
- This remains the norm a few centuries later in The Lost Fleet, when colonisation has progressed far enough to allow for governments that span multiple worlds: How much autonomy individual worlds and regions have isn't addressed in detail, but each inhabited planet within The Alliance or the Syndicate Worlds has one unified local government for that world and any outposts elsewhere in the system. Justified by the fact that individual planetary populations are extremely low, with one hundred million people being considered quite a large number for a particularly wealthy and important system, thanks to lingering cultural hang-ups over overpopulation and environmental collapse nearly turning Earth That Used to Be Better into Earth That Was.
- Most planets on Star Trek are examples of this trope. When a planet isn't united, the Federation basically considers it to be in a state of civil war. Earth throughout most of its history was presumably in civil war, and (except for some arguable periods of peace) continued to be at least until around 2150 AD (almost nine decades after first contact with the Vulcans ironically enough) when the last holdout finally joined United Earth. Some Federation planets (such as Vulcan) have had Planetary Nations virtually into antiquity.
- In the Star Trek: The Original Series episode "Patterns of Force" a Federation scientist decides to unite the planet he's observing under one government - unfortunately, he concludes that Nazism is the best way to unite the planet.
- One episode of Star Trek: The Next Generation had an aversion. The planet was ruled by two separate governments, the Kes (not to be confused with the character on Voyager) and the Prytt, who were engaged in a cold war with each other. The Kes were applying for Federation membership and Picard lampshaded this trope when he mentioned planets that join the Federation are usually unified. It's never said whether or not the Kes would be admitted but it's implied they won't be (though the implication is that the main issue is the Kes attitude towards the Prytt more than the technical fact of there being two planetary governments).
- Usually played straight in Stargate SG-1, although in most cases this is because there's really only one or two settlements of note (blame the Goa'uld). Two exceptions are Langara, which has at least three major powers, and Tegalus, which has two, and in both cases each are in a Space Cold War with their neighbors.
- Very common in Doctor Who.
- While single planetary governments are the norm in Traveller, balkanization is common enough that the Third Imperium (a very loose interstellar government) allows limited intraplanetary warfare, so long as they keep it to one planet and don't resort to nukes.
- Usually the case for human inhabited planets in Warhammer 40,000. The Imperium is so large that any given planet is usually ruled by a single governor (how he's chosen varies from planet to planet). They're usually given full control of their planet and left alone, as long as they pay their tithes and don't show signs of sedition (and they don't call for help, although that's usually less effective at getting someone's attention). However, in many cases this is just to make the paperwork easier; there are several planets where the "governor" is whichever ruler or tribal warlord was winning the day Imperial officials last visited.
- Taris from Knights of the Old Republic seems not only be a planet with one Government, it seems to be a planet of one city!
- This is a requirement to exit the Civilization stage in Spore to move onto the Space stage. Same goes for every other galactic empire out there, though they often have more than 1 planet; also Uprisings only happen for entire planets.
- Played with in Futurama in regards to Earth itself. Earth has its own overarching government (that is somehow also the American government and based on American governmental traditions), but other nations are shown to still exist with their own set of laws. And then its usually played straight when any other planets show up (which is normally Once an Episode).
- True in Ben 10 for basically every single world that isn't earth. Some have one government that covers multiple planets.