It is an established science-fiction trope, especially in something like Star Wars, that entire planets will be run by a single government. When trying to worldbuild, I began to think about how one government ruling at least 1 entire planet could be realistic. With a government with highly advanced technology, even if it were either weak or just a puppet government, could a single government actually rule an entire planet, despite the problems like rebellions and religious and ethnic violence?
It's all about travel time
And it's very possible
In the past, we have been limited in the size of nations primarily due to the speed of travel (or, more accurately, the speed of communication). It was very difficult to keep the early United States together because it took months to get information from the eastern states to the western territories. The Battle of New Orleans was fought 2 weeks after the Treaty of Ghent was signed, because the armies didn't know the war was over. As infrastructure and transportation improved in the 19th century, the feasible scale of governance rapidly grew, hence the boom in westward expansion. With 21st century technology, major world powers already maintain military presence around the globe.
Given how accessible spacecraft appear to be in the Star Wars universe, it is more than reasonable to think that a single strong government could rule a planet, star system, or even galaxy with enough wealth. An 18-wheeler can cross North America in a week, and a civilian class x3 hyperdrive ship can cross the Star Wars galaxy in 3 days.
You can give some or many planets unified governments, and keep a few divided into more subdivisions.
- How many worlds have been colonized by other species?
You have to decide how common habitable worlds are. Pearls beyond price or a dime a dozen? If they are common, colonists who want to found their own colonly look for their own planet, not one where other people already live on a different continent.
- A matter of perspective.
At times one gets the impression that many US citizens forget that they are one nation. Yet seen from outside, they clearly are. So there are administrative divisions on most planets, with district, city, and county levels, yet an outsider notices mostly the planetary government.
- One ecosphere, one government.
On the real world, mankind is slowly realizing that they can ruin the ecosphere if they are not careful. Imagine what they could do with more advanced technology and no need raise kids and retire where they do their pollution. With easy interstellar travel, some people might see a planet as a resource to be strip-mined, others see as a home. There will be conflicts unless there is a central government per planet.
The occasional adventure could center on worlds which do not have unified governments. "Why did you land here if you want to deliver your goods across the border? You'll have to go back into space, even leave the system for a quick jaunt if you don't want to be taxed as intercontinental trade."
Many countries in the current day are implausibly large by ancient standards, and exert an implausibly large degree of control. This turns on advancing technology. Communications, travel, and collation of data are crucial technology.
Remember that the government will break down the world into reasonable sized chunks of ease of administration. Even towns and villages will have their local authorities that deal with many problems within the scope of the village/town.
Quite small regions have been riven by rebellion and violence. The government may in fact deploy forces from other regions specifically because they don't have any skin in the game except their paychecks.
It depends - how did it start
Situation 1 - origin planet with multiple civilisations developing separately (eg Earth). As many previous questions have covered, until modern(ish) technology was available, there was no possibility of a "world government" simply because regular, timely communication between the various parts of the planet was impossible. Hence there will always be lots of different nations to begin with in such a situation and it is a matter of whether they are willing to eventually find more common ground than points of difference whether they unite, once the technology exists to make such an option possible. Without a crystal ball we don't know whether our single known example will unite or remain fragmented, either is a future possibility.
Situation 2 - colonised planet from single source. If a single government / corporation / settlers' cooperative founds a colony on a planet and settlement spreads out, I suggest it is likely to start as one government and remain as one government. It makes far more sense to retain one government in order to keep common standards of interoperability, consistent legal code, recognition of training qualifications, maintenance of spaceport and orbital traffic, maintenance of commsats / weather sats... There will definitely be different levels of government for once it spreads out enough (eg federal, state, local or equivalent) but the only reason a region would want to secede would be if it was being so badly mistreated that the hassle of replacing all top-level government functions would be easier than staying in the union. (Yes, this does include the possibility of some self-centred idiot politician/s convincing the local population this is the situation when it actually isn't and downplaying the inevitable consequences.)
Situation 3 - colonised planet from multiple sources. If multiple sources settle a planet simultaneously then the outcome is uncertain. It could be that the colonists find they have more in common with their local neighbours than the group that sent them and unify, or it could be that they remain separate nations on the same newly colonised world. A great deal will depend on the differences in culture (including language) between the different colonies, how "successful" each colony is at various times and how the colonies are treated by the government or other entity that sent them. For example, if the various settlers all speak the same language, they are insufficiently supported by the group that sent them and one colony provides vitally needed aid to the other/s then unification is highly likely. If they all speak different languages, have significantly different values for personal freedom and are all strongly supported from "home" then they are likely to remain separate.
In summary, how a planet's civilisation/s started will determine how likely they are to unify or remain unified.
I would say that it is entirely plausible for one government to rule one planet. I would even argue that it is the most likely logical progression for governance.
Outside factors frequently play a critical if not indispensable role in the destabilization of empires. Wild ideas and tech, abused neighbors hungry for revenge, aggressive neighbors anxious to steal what the empire has, and desperate migrations caused by catastrophes have contributed to many societies changing or collapsing.
Removing external threats simplifies the process of ruling a world government. You can oppress people with little concern that someone will support their revolt, or that the tale will be told and the truth will come out. You can control all supplies, all weapons, all freedoms, all technological progression and most importantly you can erase the past and write all the history books to your liking. The only voice people hear is yours. Of course, innovation will suffer in such a system, but if you control the whole world, you logically should restrict innovation so as to prevent any destabilizing elements from disrupting your control on society. After all, once you are in control, the status quo naturally involves you STAYING in control.
Of course, in a world with spaceships flying in from other worlds, this starts to be a problem. But fear not, you restrict access to the planet to trade stations and orbital bases and all that messy stuff gets kept out. A logical world government would likely need to maintain strict separation between the outside and the surface. Failing to do so opens you up to the same kind of pressures societies experienced when colonized by foreign powers. Much like Japan, restrict trade and cultural exchange with the outside and maintain tight control on the advancements you need to stay competitive with other civilizations
On Earth, every recognized sovereign state except for the Vatican City has one or more levels of administrative subdivisions. Larger states have from one to six levels of subordinate administration, or two to seven levels of government in all.
Leaders of subdivisions within a country can be elected by the residents, appointed from above, hereditary, randomly selected, usurp power, or gain thier positons in o ther ways. There are many examples of states with several differnt types of subordinate governments.
In most of the USA there are four levels of governments. The federal government conducts diplomacy, makes war, and has many other functions for the general welfare. State governments issue driver's licenses and have many functions for the general welfare. County governments maintain recordsof births, marriages, and real estate deals and have many functions for the general welfare. Municipal governments clean streets, collect trash, often own utility companies, and have many functions for the general welfare.
All levels of government have courts to try violations of their laws and rules. Many projects are jointly managed by two or more levelsof government.
And there are other government institutions such as school districts, various authorities, and tribal governments.
Most of the Roman Empire's land was divided into city states which had elected councils and magistrtes. A subdivision within a city state was called a pagus. Governors of provinces commanded the military in the provinces and supervised the city governments. And above them were the emperor, the senate, and the popular assembly at Rome. So there were four levels of government in the early Roman Empire.
In the later Roman Empire the miltary and civilian functions of governors were separated and given to diffferent officials. The number of provinces was multiplied, and provinces were grouped into dioceses ruled by appointed vicarsd which were part of prefectures ruledd by the four praetorian prefects under the emperor(s). Thus the later Roman Empire had six levels of government.
So I can imagine that a hypothetical united world government might might take the diplomatic and military powers of the national governments while leaving them other powers.
And that world government might be directly above the formerly independent national governments, or it might have one or more levels of government between it and the national governments.
For example there could be continental governments over each of the four, five, six, or seven continents recognized by various governments. And there could ocean governments ruling all the lands whose waters flow into each ocean of the world. The lands ruled by the continental and oceanic governments would overlap, so that subordinate governments could communicate with the world government though either, or both, and vice versa.
And maybe the world government would revive some of the great empires of the past as an intermediate level of government between the natioal governments at itself. And of course almost every present day national government has been part of one or more emperies in the past.
And the advantage of overlapping areas of rule by governments above the former national governments is for lawsuits. If people take a case to higher and higher leavels of courts until they reach the supreme court equivalent of their nation, they then have a choice of two or more even higher courts to take the case to, if th two parties can agree on which one. So adding another level of courts will increase the probability that one side will give up trying and not take the case to the Supreme World Court, thus lowering its caseload.
And a world government should be able to last more or less forever, so long as it has a monoloply military force. For example, all the military and civilian bodyguards of all the subordinate rulers should be world bodyguard service, working for the world goernment and assigned by it to be the bodyguards of the subordinate rulers.
I would definitely say its possible.
There are already big world organizations like NATO and UN that are already successful. And in its peak the British Empire controlled almost a quarter of the worlds land area, and housed 23% of the world's population. A United World government is certainly possible, but a government like that would probably be more complex than any government today in order to sort out all the problems of the entire population. And this world-country would probably be split into many sub-countries and sub-governments, kind of like how the US is split into states with their own sub-governments, except these states could be regions of the world, like maybe the Middle East as one or Europe as another. it would probably not be one identity, you probably wouldn't identify as a citizen of United Earth, more like a citizen of you sub-division. These mega-states would probably also have further sub-divisions, maybe with their own sub-sub-governments.
So yes, a united world government is certainly possible, although it is definitely something for the future, and probably not possible today, as you would probably need to sort out the differences in things like ideology, culture, laws, customs, etc. And things like a global currency would need to be worked out. You would also need to make a system for voting the leaders of the world government that at least most people agree on. It may not be a democracy but rather something else, but of course nothing is stopping democracy from working. Maybe they have elections but instead of republican, democrat, that sorta thing, you would have like a communist party and democratic party, etc. Maybe each of these world-states would have radically different cultures. there are endless possibilities, and it certainly would not be easy to make a united world government, you would need to unite very different parts of the world, and it would probably take a long time, maybe decades or centuries.
Ruling = protection racket?
"Ruling" is an imprecise term. Does that mean careful granular governance, discussing school day hours, tax rates for various business, the number of pennies to mint, etc? Or does it mean a glorified protection racket, extorting money with the threat of violence. Either one could constitute ruling. If I must pay tax to the imperial overlord or get some Rods from God in my yard, the imps are my rulers. This kind of generally uninvolved government would be easiest to do planet wide because all you do is collect tax and sometimes mete out punishment.
There may be other more local rulers who are less scary and more involved in the day to day affairs of your area. The planetary government might actually be that for their local area. And your Planetary Empire protection racket might be protecting the planet! If the tax collected from the provinces is used for defense of the planet as conducted by the Emperor that may be a good thing for all inhabitants of the planet, whether they appreciate it or not.
In a sense, there are two facets to this question: the scale of the setting and can one government rule a world.
TL;DR: Can one government rule a planet? Sure.
The longer answer involve logistics and delegation and a thoroughly unhealthy amount of politics (or weapons).
To rule an area, one needs to be able to aggregate information to a central location, process it, and respond with a course of action. The faster this can be done, the larger the area one could plausibly rule over. It's a gross simplification and does not take the people one is ruling over into account, but it is a start.
With advanced enough communications technology, information can cross a planet in minutes -- we already do this with the internet here. The key for your world government would be a robust communications network that could reliably do this.
Processing is already feasible here. Between people using their intuition and computer algorithms processing the large amounts of data received, the data coming in from all over the world can be processed and checked over. I might say that for a world government, a bit more raw processing power might be needed, but that is potentially solved with a bigger computer for now.
Also, if the world government is delegating regional authority to a regional group (like a state/province/territory), then that may reduce the information that needs to be gone through as the regional offices will handle the regional affairs and only kick up what needs to be.
Responding is a people thing. As long as there are enough people authorized to make the decisions and the time to do so, then things should work. The issue will be dealing with things in a timely manner to have at least the appearance of a functional government. For this, it's about transportation and logistics technologies -- the ability to move resources around the planet efficiently. We can do it somewhat now, but it could probably be better.
I've avoided trying to outline specific governments to limit the length of the reply. Some governments will delegate some power to local governments to better serve their people while others will centralize everything into a global capital for more selfish reasons. But regardless of how
The Galactic Stage
The thing about a galactic scale setting is that a planet is just not as significant as it would be if your setting was the planet itself, or its solar system. There is likely not a ton of thought on the government of each individual planet unless it is significant in the setting.
Realistically it is a matter of scale and conservation of detail.