So, I'm well aware that Sci-fi Writers Have No Sense of Scale. This is an effort to avert this for intragalactic conquest.

My mighty space navy has crushed a solar system's defensive fleet, and now control the space around a planet similar to Earth in population and distribution thereof. It's time to send in the troops to take control of all positions of relative importance so that the planet can be integrated into my growing empire.

My invasion troops are well-equipped; any one soldier could expect to win with minimal injury in a stand-up fight against one of the defenders' armour units (main battle tank or equivalent).


  • I need boots on the ground because I want to start integrating the planet into my empire; threatening them with orbital bombardment has just encouraged passive resistance - they won't attack, but they also won't do anything useful for me.
  • Pursuant to the above, I would like the end result to be a revenue-positive addition to my empire. I'd like to add their economy to my own and (obviously after some rebuilding) have it be a contributing non-voting province. (In fairness, my home planets are non-voting as well. My empire subscribes to the One Man, One Vote philosophy. I am the Man, and the Vote is mine.)
  • I will also need to send administrators after local resistance has been crushed.
  • My soldiers, for all their impressive armour and weaponry, are intellectually and perceptually basically human-equivalent. They aren't any more capable of maintaining focus on multiple things than a well-trained soldier of the other side.

How many troops will I need to deliver to secure a planet of seven billion? If I want to do this expeditiously, how many drop ships would I reasonably need to deploy (for their geographical distribution).

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    $\begingroup$ What's the purpose of the occupation? Do you simply want to prevent the defeated foes from organizing their resistance (for example, what the Americans do in Afghanistan), do you want to rule the conquered planet (as the British did in India), or do you want to convert the new conquest into a productive province of the Empire (as, for the example, the Romans did in Gaul)? As for the strength or weakness of each individual soldier, having the capacity to defeat a tank is irrelevant -- they won't be facing tanks. What they will be confronted with is IEDs, sawed-off shotguns and RPGs. $\endgroup$ – AlexP Feb 5 at 19:04
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    $\begingroup$ Well then, you must be prepared to be a better ruler than the previous administrations. The Indians allowed the British to rule India because the British administration was objectively better than the feudal regime they replaced. The Gauls agreed to become Romans because the condition of a Roman citizen was infinitely preferable to the condition of a barbarian. (Consider for a moment a Gaulish family; the wife learns that Roman women have rights, they can own property, they can engage in trade, they cannot be married against their will: how long until the wife decides that she is Roman?) $\endgroup$ – AlexP Feb 5 at 19:11
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    $\begingroup$ @AlexP there were some revolts in India, and some of them were quite significant. $\endgroup$ – SJuan76 Feb 6 at 9:44
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    $\begingroup$ An important question would be how the conquered planet is. For example, if it has a complex economy it is easier to control it than if every household lives independently from the others, as the invaders can control the exchange of goods. A planet with mountains is more difficult to manage than a big praire... $\endgroup$ – SJuan76 Feb 6 at 9:48
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    $\begingroup$ Careful, guys. OP wants to know how to take over a defenseless "Earth-like" planet, and coincidentally our "Earth-like" planet has no space defenses... $\endgroup$ – Lord Farquaad Feb 6 at 19:07

13 Answers 13


No ground troops at all.

You're a merciless galactic emperor. You don't need to be popular among a newly conquered people. You won't be popular anyway, regardless of how much you try. You merely need to deny them a realistic political alternative.

Appoint a local quisling with some existing plausible claim to rule as your viceroy. Let them do the hard work of dodging assassins, oppressing or co-opting the opposition, and integrating their world into your empire.

High ranking collaborator families should be housed offworld, effectively hostaged by the empire to ensure loyalty. The reward for loyalty is that their children will be among the ruling class of the empire.

Rotate a few of your battleships on station for a few decades to keep control. It will keep the quisling reasonably honest, and you are likely to need to impose several mass reprisals until the collaborator regime is stable. No warnings, no discussion - the planet continues to show impeccable behavior at all times, and to obey the collaborator government, or --blam!-- goes another city. Plenty of cities, after all, and more being built all the time.

  • $\begingroup$ You may appoint someone to make the planet an economic asset, and they may try to do so, but that doesn't mean that they'll be acceptably successful. And the orbital strikes don't help either, as they don't positively encourage the populace to cooperate - "the beatings will continue until morale improves". And at the end of the day, you're only killing your own labor force. $\endgroup$ – LastStar007 Feb 7 at 6:02

Do what the Assyrians did. Evict the conquered people, and spread them throughout your empire. Move your own loyal citizens to their world; maybe as a reward for your victorious soldiers. Don't allow the evicted to form enclaves. In a generation or two, their culture will be no more and they will cease to put up any real resistance.

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    $\begingroup$ There's no way you could lift every single human being off the earth without the cumulative heat of all those spaceship engines setting down and taking off baking the planet to a crisp and wiping out all life. $\endgroup$ – Tom O'Daighre Feb 5 at 21:50
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    $\begingroup$ I like this conceptually, but it doesn't answer my manpower questions, so it's not, strictly speaking, an answer. :S $\endgroup$ – jdunlop Feb 5 at 22:51
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    $\begingroup$ I think it does though. You don't need a massive occupying force sticking around indefinitely, because you aren't trying to permanently pacify an unruly populace. You only need enough to protect the eviction operations. And as it progresses, you will need fewer and fewer soldiers because they will be guarding fewer and fewer possible threats. $\endgroup$ – Ryan_L Feb 5 at 23:01
  • $\begingroup$ Just to add to that - this has been a common practice throughout the ages. For example, the Ottoman empire did this regularly - claiming a new location and moving the people there to (potentially) the other side of the empire. Then moving some other newly conquered people in their place. It works out because both will be sent somewhere they can live - you'd have infrastructure and probably even housing and other facilities left over but the moved population doesn't know the land well and doesn't have friends around, so a rebellion is harder to start and easier to put down. $\endgroup$ – VLAZ Feb 6 at 7:58
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    $\begingroup$ Also, this may not work on Jews. :) $\endgroup$ – AFischbein Feb 6 at 14:28

You can't do it with troops alone.

However, it can be done either by the slow method or the fast method.

In line with @AlexP's OP comments, the slow method would involve the carrot as well as the stick. Take over a small, defensible country. England would do for this since the water around it meas that you don't have to burn a "no man's zone" around it. Defend it from outside attacks with troops, installations and orbital strikes for big attacks.

Then use your technology to make their lives much better. Wait for things to calm down and then start offering the benefits to other nations. Some strikes will be necessary against the belligerent but no full scale invasions.

Once a significant majority of the population is under your rule, recruit troops from locals to clean out the pockets of resistance.

You might not even have to invade the first country if you can get them to join for benefits. Perhaps, operate the world using a pyramid scheme where any joined country gets a percentage of the profits from any nation that joins after them.

The other method is faster but not as profitable: remove the current population and bring in your own. Removal method is dealer's choice: bio weapon, chemical weapons, nukes, or a big rock. The native infrastructure is so comparatively low tech that you are going to have to replace it anyway so it doesn't matter if it gets broken.

If the invader has a slow population growth, the fist method gives the best long term profits. If the aliens BLB (Breed Like Bunnies) then the second method gives them resources and some place do their thing.

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    $\begingroup$ You may not care about the infrastructure, but the ecology is probably useful. Enough nukes to remove the current population is not going to be good for the environment, and is likely to leave otherwise useful places contaminated. One big rock will wipe out everything, not just the intelligent inhabitants. $\endgroup$ – David Thornley Feb 5 at 22:41
  • $\begingroup$ @DavidThornley, that's why the slow method is more profitable. I only listed the fast method as a contrast and to indicate that there may be some specific cases where it might work. $\endgroup$ – ShadoCat Feb 5 at 22:55
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    $\begingroup$ Take over a small, defensible country. England would do for this since the water around it meas that you don't have to burn a "no man's zone" around it. The problem with that approach is that you're deliberately placing yourself in an encirclement situation. You're completely surrounded... and a planet that's mustered up a space fleet isn't likely to just sit back and wait... or be stopped by 20 miles of Channel water. $\endgroup$ – HopelessN00b Feb 6 at 4:44
  • $\begingroup$ @HopelessN00b, the thing is: the attacker is the one with the space fleet. That means that any attempt at encirclement can be smashed from orbit. This is leveraging tech and position to minimize the number of troops needed. $\endgroup$ – ShadoCat Feb 6 at 23:51

There's a distinct lack of precedent present in the majority of the answers so far. Many of them were ultimately unsuccessful because the local population never truly accepted the oppressors. They all seem like good ideas on paper but ultimately they lack the backbone of any good occupation.


Yes, occupation is about administration and record taking.

Truly the most insidious example of a successful occupation would be the Soviet Union's takeover of the Eastern Block (Poland etc). They're occupation was terrifying in it's efficiency compared with the previous Nazi occupation. In fact, it makes the Nazi occupation look like an appetiser; despite all the horrors of the holocaust, it was relatively poorly managed and resistance was certainly possible. The Soviets meanwhile had had a decade of practice on their own people back in Russia.

Lets pick it apart stage by stage.

First the armed forces annihilated the local military presence - in this situation it was the occupying forces of the Third Reich but it could have been the local populations military as well. As the front line passed, the true power of the soviet union came into action. For every frontline division that was involved in fighting, there was a second purely administrative occupation force. The Soviet invasion of europe was a masterclass of how to occupy. They put as much thought into this second wave as they did the front line fighting troops.

Seize power The soviets openly invited local resistance and hiding government officials to greet their liberators and discuss the future. They had survived 6 years of nazi occupation. They were all duped, imprisoned and murdered leaving the populace with no figurehead to rally behind.

Documentation Upon entering newly seized territory, every single inhabitant was documented and given fresh papers.

Limit travel and seize communication Once registered, permanent road blocks and check points were installed. Anyone who didn't report for new papers will now be unable to move freely in the streets and will die. In a modern setting, this would apply to communication as well. How can you organise any resistance if you can't leave your neighbourhood even with the correct papers and there are no phone lines or mail services? Better yet, allow limited distance communication but wire tap it all so you can pin down where resistance is likely.

Seize the media All local media sources are ruthlessly taken over or hunted down, preventing dissident opinions from being broadcast. These are quickly replaced with propaganda - finely tuned to read and sound like local people rather than the oppressors. In many cases, underground newspapers were secretly overtaken by the soviets in order to control the resistance forces from the inside, rather than defend against them.

Create a neighbourhood watch system At the height of the soviet rein, it was estimated that every single person had 3 people watching them and reporting on them. The bureaucracy is terrifying. These could be government officials and secret police but also family and friends. With a reward system for identifying conspirators (better rations, quality of life, etc) it's easy to make people betray each other.

Run this for a few decades and you get a near enough wiped out and terrified older generation and a young and brainwashed younger one who doesn't know any better. This is essentially the real life basis for George Orwell's 1984 and a prediction of what was to come of occupied Eastern Europe if allowed to continue as it did in the late 40s. Assuming the economy doesn't collapse and lead to revolution, you now have a near enough permanent and stable placid population to do your bidding.

It's utterly unfathomable. But it happened.

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    $\begingroup$ Add a dash of Chinese-style Social Credit, and you're good to go! $\endgroup$ – Eth Feb 6 at 16:15

There is a difference between conquering a planet (fighting against the regular army of a planet on open field) and enforcing the rule on it (fighting against guerrilla, dealing with civil unrests and so on).

For the first part, during the first WW Germany mobilized 13M people out of a population of 67M, about 1 on five... For an planet of 7 bilions, we can assume the defending army will be 1 bilion strong. In case of a full scale war, even assuming you have the control of the skies and your soldiers are at the same level of an enemy tank, you would need in the best case an order of magnitude in the tens of milions soldiers.

You will have a better time using a divide and conquer strategy (as Romans did to conquer the ancient Greek cities): even if it is probable that the enemy world will try to unite against a big external menace, there will surely be different factions, each one with its own agenda.
If you control the orbit (and of course drop bombs on whatever on the surface seems a launchpad for rockets), everybody on the planet will know that the outcome of the war will not be subverted (at least, not in the short term): many people on the planet will surely try to ponder hot to take advantage of this situation.
So, just try to entice some of them, promising them the power after the victory (or - if you're a really vicious evil emperor - less harsh punishments). Wait for the intestine war to start and then send a small elite force to the ground to help your faction (you will find lots of similar strategies in history books). You can also help them bombing their enemies from the orbit.

This way, as already hinted in the other answers, the ruling faction of the planet will owe its authority to you and that be loyal to you. Just don't forget to keep (for a generation at least) some battle-ready battleships in the orbit of the planet in case your quislings decide not to obey anymore.


You are in luck! Terrans have a long history of invading each-other in glorious bouts of violent imperialism. If you want to know what works on them, simply look at what worked.

Copy the methods of successful empires in Earth history

This answer already describes the methods of the Soviet Union. This is a good place to start, as its rule went unchallenged (until its implosion, but we are not concerned about the fate of the whole empire here).

The British Empire was possibly the largest one in Earth history, and its control of oceans can help as parallel for your control of space. Notable things they did that worked:

Foster a local elite. The easiest way is to take people already in a position of power, and make them rule the others for you. Those who don't want to will be eliminated, you will find volunteers to replace them if needed. Use your power to keep them in power and in your debt, and pay them well enough for them to stand head and shoulders above the rabble.

From there, create a pyramid class system. This is very important, all successful oppressive empires were built on it. In its simplest form, you have your Citizens with the highest status, the local Citizens - second-class, but ruling everyone else for you, the oppressed Rabble, and some even more oppressed class so the Rabble has demotion to fear and someone to feel superior to. But really successful ones tend to use a more complex system: more classes, but also competing classes. So not only individual will compete with each-other for your good graces and the privileges going with it, but entire groups will also fight each-other to try and get higher in the pyramid by stepping on other people's faces. While everyone fight each-other to be your lackey, uniting against you will be impossible. Note that this isn't only in the upper levels of the pyramid. Even at the lower levels, people will fight each-other to not be at the bottom level.

Which leads us to the next point: foster hatreds. Cultural, racial, religious, geographic, national, the more the merrier! Humans have an instinctive "us vs them" mentality, use this to keep them divided. As the distant overlord, they may resent you but their carefully nurtured hatred of each-other will always be stronger - and it is self-sustaining! This will be one of your most powerful tools to keep the pyramid scheme working. And this helps shift the blame of your oppression to each-other, especially if you use them as local occupation peace-keeping forces.

Remember, small, local genocides are OK if the need arise, as long as you don't overdo it.

And of course, pervert local institutions to your own ends. If there is a caste system, turn the ruler/ruled/you-foul-my-air-miserable-wretch knob to eleven. If there are religious institutions, make sure the (surviving) high priests are now using a message compatible with your rule, or diffuse hatred of other groups, which is almost as good. If there are local administrations or hierarchies, take them over, etc...

An old trick, cultural domination is also important: use your control of media for bringing your culture, and keep the message that it is superior to their own primitive local cultures. Send the children of the local elites local Imperial schools, and to universities on your core worlds, to be formed alongside your own ruling Citizens. They will never be of equal status, of course, but they will think they are part of your empire, and be trained to think as such.

Another old trick: form local soldiers and send them fight/occupy different worlds. That way, not only you get more (and more sacrifiable) soldiers, but you get them to fight for you, thinking themselves as your soldiers, even going as far as sacrificing their lives for the honor of protecting your oppressive rule.

Now, those cunning humans have come up with new, interesting systems of oppression.

You can go for 1984, for example, if you are a more hands-on kind of oppressor. You need to build a (or rather, several) totalitarian system using hatred, systematic rewriting of reality through the media, thought police and eternal war to keep them in check.

You can also go for the more modern Social Credit system that one government is kind enough to be experimenting on their own population for you. You can see this as an amelioration of the 1984 system, using the wonders of mass communication and mass data treatment technologies. Possibly the most efficient thing they ever came up with, though experimental trials are still running at the moment of writing this, and it may not work everywhere on Earth due to lack of infrastructure.

With that, in one or two generations, Earth should be firmly in your grasp. There may be a few pockets of unrest or even outright rebellion here and there, but you can use that to help the "hate-each-other-and-compete-for-your-favours" part of the scheme, by sending opposed groups fight them off. And if it degenerates into an all-out uprising, well, you still have orbital control. Use your elite forces, air superiority and orbital strike platforms to protect your Imperial districts, negotiate with the many groups that hate each-other more than you, and they will spend more time horribly killing each-other than killing you. You may loose a few Imperial Citizens, but heh, you can always bring more to replace them. At worst, you can re-invade the planet.

But what if there is a really, really bad rebellion?

If something went very, very wrong, for example psyops teams from a rival empire have sown organized rebellion, this may not be quite enough. Fortunately, humans came up and have somewhat refined another method for quelling rebellions: the Terror.

Now, this can take several useful forms, the original one being the political Terror. But we are talking here about the military form, used to hit a population so hard it cannot physically sustain an insurgency anymore.

This is rather simple, really, but you have to do it right. First, hit what allows populations to sustain local insurgent forces: hospitals, urban concentrations, food production... Then, make sure you commit atrocities on local populations while fighting insurgents. Here again, having local groups hating each-other is especially useful. Then, use widespread torture. Not as an information-gathering tool (though that's one of the best disguises), as it is terrible at this job. But it is one of the most efficient tools to terrorize a population.

And never forget: hit the less extremist group first. You want to escalate the situation, and make sure that the population understands that it has a choice between your admittedly horrible but more or less stable rule, and the even more horrible and violent rule of hate-driven fanatics exposing them to atrocities from both your forces and said fanatics. Be the lesser evil by making sure you destroy lesser evils than you first. And don't worry, surviving humans are easy to escalate and join extremists (including your forces) when caught in that.

But only use it if things really go bad, this will put a dent in the value of the planet. Having a few zones like that in your empire may be useful to train soldiers - and atrocities committed in your name against local civilians a cheap way to build esprit de corps. Not as good as modern training, and possibly counter-productive for your best troops, but cheap and good enough if you need cannon fodder. But you may want to avoid those zones if you can, they can be quite a bother to sort out in the long term.

Note that those human empires tend to fall apart long-term for the same reasons that make them stable short-term: your top of the pyramid, the ruling class on your homeworlds, get used to the resources they get from the peripheries and lower classes, but exploitation of provinces tend to be unsustainable over generations (because no-one will make the effort to collect less to make it sustainable over longer than they are here in the first place). As such, at some point peripheries have been exploited to the ground, and cannot produce more.

At this point, you have to conquer more, as your core ruling class will turn on you if you don't keep their funding at the same level or more. And at some point, the empire either runs out of places to conquer or become too big to manage.

Unless something else topple them violently before, this is generally how human empires fall apart. But maybe you'll do better, who knows?


A platoon per independent leader.

You don't need to control the populace, just the people who govern them.

As much as possible, you should maintain the local power structure, just add another level on top. You. Deploy a platoon of Space Marines to "guard" whoever was in charge of this planet, whilst also conveniently reminding them who they now work for.

Simultaneously, bring their family into the fold back on one of your core planets. Give then an Imperial education and lifestyle befitting the family of a planetary governor. This way you are already Indoctrinating the next leader about the right way to do things and using them as hostages to keep the current governor in line.

Then, give the governor some modest quotas and let him do his thing. People are much more likely to follow if it's someone they've known all their lives who are still giving the orders.

You may have to do this multiple times if it's some backwards planet with multiple independent nations, but if you get a few dissenters, that's when you start glassing things from orbit or deploying marines to aid the loyalist nations in subjugating their fellows.

After that, you just have the local media and education systems start pumping out Imperial propaganda and culture to convert the next generation.


Depends on how much you expect the population to resist, and whether you expect there to be a ground invasion or not.

For a relatively passive or non-hostile population, you could look at ratios of police to civilians in the real world. For example, in the US, it's about 1:500. (~670,000 sworn officers for ~325 million residents.) I'd say that's your (unrealistically small) minimum for purposes of keeping the peace, if the planet basically gives up, doesn't fight a ground war or conduct an insurgency. For an occupied population of 7 billion, that works out to 14 million occupying soldiers, as your baseline, keep-the-peace-during-peacetime requirements.

Of course, you won't be at peace initially, and you'll probably want to bring more soldiers just in case (it's always better to have too many heavily-armed killers at your beck and call than too few), and you probably don't want to just assume you'll encounter a passive population, because that never really happens. Even the most legitimate governments with wide popular support have troublemakers occasionally killing their assorted agents, and you'll have the issue of how to replace forces lost to attrition.

So, I'd suggest relying on a military model, and the latest Iraq war is probably a good model. The invaders had overwhelming technological and operational superiority (air superiority and so on) and brought about 300,000 troops against a population of ~26 million, for a ratio of about 1:85. As in your scenario, the actual ground war was expected to be a foregone conclusion, which it was, but the invaders still brought an order of battle comparable to the vastly inferior Iraqi armed forces (~375,000) at the time. After the invasion, many of those soldiers went home, but they were supplemented by 850,000 Iraqi security forces and the Kurdish militia forces numbering ~70,000 (and administering about a third of the country). Ultimately, during the Iraqi occupation, there were approximately 1 million allied soldiers and paramilitary forces to control a population of ~26 million, for a ratio of approximately 1:26. That would be over a quarter billion occupiers in your invasion. Yours would have greater superiority over the opposing forces than the mostly Iraqi security forces did in Gulf War II, but then again, you'll have a more hostile population to deal with, probably won't be able to recruit many local forces to help, and have to deal with replacing attrition loses... so I'd keep a similar ratio.

I'd suggest you would probably want a similar approach. You'll want a similar order of battle to the opposing forces, and a ratio of occupying forces comparable to what the US had during the height of the Iraq occupation. The US had advantages you won't, in being able to install a local government and use their forces for the vast majority of the occupying force. That seems unlikely to apply in an alien invasion scenario, and it's also unlikely that you'll get the population to fraction along sectarian lines, where the insurgents are solely from a minority group of the population.

To determine what the opposing force will be, I'd look at the total war model, WWII, being a recent one we have lots of good data for. In those conflicts, approximately 20% of the population of the invaded countries became members of the armed forces. In your case, I'd double that. (I doubt that the planet you're invading would exclude women from combat, like we silly humans did in WWII.) That would give you an opposing force of about 2.8 billion to contend with initially, and yes, you want a comparable force. Even with technological and operational superiority, offensive fighting while significantly outnumbered rarely works out well. We've never seen a planet-wide alien invasion, so we don't have good data on how that would work - maybe you could get away with less by conquering one continent at a time or something like that, or maybe you'd need more because the defenders would take up strong defensive positions, engage in asymmetrical warfare and keep your forces bogged down and surrounded on all sides in order to slowly grind your forces down.

Bottom line, I'd expect you would want to take a force comparable to the opposing forces, which you could expect to be ~40% of the population, or about 2.8 billion. You could probably use your advantages to drop your invading forces to ~2 billion or so, but you don't want to drop it much lower than that, or your risk finding your forces outnumbered significantly at points, which will result in heavy loses or a slow, grinding defensive operation, both of which are very bad for you as an invader. Once the war is won, you should expect a widespread insurgent activity, for which you'll probably want to maintain an occupying force in the hundreds of millions (~250 million going by the Gulf War II model).

Sure makes the idea of glassing the planet from space or biological warfare more appealing, doesn't it?

  • $\begingroup$ There are countless writers (many of them wrong) who speculated how many troops you "need" for counterinsurgency. 20 per 1,000 people is sometimes quoted. $\endgroup$ – o.m. Feb 6 at 5:20

Send troops to capture the means of energy production - the power stations (basic really), and of course the fuel depots (and the means to re-supply the power). The water networks are also terribly usefull.

At the same time you'll be hitting the communication networks by way of obliterating existing networks, including satelite, cable, radio and taking control of emergency broadcast networks (EBN).

Tell the people through the EBN's worldwide that you have control of the means of food distribution, power distribution, and water production. They should comply with the Emperor's dictates, or the their civilisation will be rendered innert - any resistance can be co-opted to fight - given military training, and positions of power....... In time the rest will see.

So, controlled by your military, mediated by converts, finaly your burearocrats can enter and take charge - promoting any who fall-in with the regime, ... and the rebels? If you can't co-opt them , then you kill them, publically - but always in a way that shows the benefits of falling-in with the regime.


Depends on methods and the state of the planet really.

If your invaders merely have bigger guns, treat the locals like trash and steal everything of note, there going to have a hard time keeping order however strong they are, as the locals would be highly motivated to resist.

Also just because your solders have a consider tech edge, it doesn't mean they are indestructible. Ambush, sabotage and psychological warfare can narrow gaps in power, and it all too possible that your own solders might switch sides (your a tyranny after all), or even worse someone with knowledge of how all your fancy tech works. At which point you've got everything you need for a dangerous rebellion.

On the planet side of things, a truly united and peaceful planet with a strong central culture and a strong tradition of Democracy would be far tougher to control that one made of hundred of separate states that hate each others guts and are ruled by tyrants.

It likely worth grabbing the history books on historic empires and learning how they operated and garrisoned. The British Empire, Mongolians and Roman Empire are all pretty well documented. So see if you can find some relevant reference material that way.


I'd look at how Starship troopers handled the matter. The book invented the concept of power armor, which the ground troops wore as standard issue, and they were advanced enough to allow for patrols to consider a one trooper per square kilometer "Dangerously Close".

If we work this out that troopers can cover about 2 square kilometers of land, then you would need about 148,940,000 (total land area of Earth) /2 kilometers ^ 2 per person = 74,470,000 individuals for patrol duty (by comparison, the current active duty of the United States Army is just under 500,000 individuals. The entire United States Military is estimated to have about 1.3 million individuals in active duty, and is the third largest standing military in the world, and the Army is the largest branch.). Again this assumes future tech in play that allows such division of labor, and that number can be brought down if the Power Armor makes greater distances available.

This of course does not include logistics and support (Armies march on their stomachs is still in play) which typically requires a force of 4 men for every 1 man on the front line... again, allowing for a wider territory per front line man, you could narrow that number.

For ship deployment, ships are much bigger and will also be staffed to some degree, also increasing the number. A Nimitz Class Super-Carrier and the Ford Class replacements are the largest naval ships on earth. The Nimitz has a crew compliment of about 6,000 and the Ford is expected to be about 4,000 and the non-air wing crew compliment is 600 fewer than the 3,100 of the Nimitz, mostly due to better technology for many jobs. Carriers never operate alone and have several screening ships including a few missile cruisers, a Destroyer Group, and several patrol subs and many support craft. Space Craft with Carrier functionallity are better seen as Battle Ships on the Streets, Carrier in the Sheets (Because Battle Carriers in wet navies are stupid and don't work and Battlestars are trade marked. The fact that your flight deck is inside you ship, rather than on top of it in a space ship means you have all this wonderful hull space to mount guns. You can have a lovely bunch of laser guns, standing in rows. Big ones! Small ones! Some as big as your head!).

Star Wars probably has a better one where thinking of the capital ships are better seen as forward operating bases, rather than air craft carriers (still don't forget the compliment) which is probably similarly staffed as a carrier, but are more spacious allowing for tank repairs and what have you. I would suggest with this thinking and possible troop sizes to hold the whole planet, you could easily forgo that frightening 4:1 ratio for ground troop estimates and do them in your big ships. I would say a good ration here would be 1 of these ships per Continent, or 1 per 2 sub continents. For drop ships, it would be difficult to assess as you need to have a few drop zones per continent. I would suggest looking into operational unites, see compare that with the territorial range of one unit total (square kilometers per person times number of people in unit, and have maybe two or three per drop point or unit covered region (in case of breaks or drop ship losses).


Surprisingly few, if you play your cards right

Building on @Kyyshak and @McTrooper's answers, and recalling the maneuvering in the Lost Stars book series, I got the idea to sandbag your invasion force. On a ballpark, this method only requires a navy the size of their largest state.

Step one: acquire power in the shadows

At first send over only a handful of ships and throw your support behind a decently powerful local faction, ideally one that pays some lip service to freedom and democracy. Then as the civil war erupts, all the potential threats whittle each other away and you help your chosen faction to victory. Meanwhile, show your full military might to the faction's leaders so they know who's in charge. The result is that the populace is duped into thinking they're working for locals, while you're really pulling the strings. You can enhance the populace's loyalty here by offering small quality of life improvements through the favored faction.

Step two: solidify control

Start installing your own agents as council members, bureaucratic executives, newspaper owners, etc; in short, people with power disproportionate to their recognition. Start the propaganda wheels rolling. It might also be a good idea to move some of your own citizens to the new planet.

Step three: begin exploitation

Do not begin this step for a couple years after step 1. Impose a tax, again through the local faction. For maximum effect, give the populace something to show for their taxes at first: a new bit of technology, an expanded (but not too much) military, mutual-defense agreements, something big for them but little for you. People react to tax increases, not as much old taxes around for another year. By this time, the planet should be producing an economic output for you, so your question is answered. But I'd still recommend a follow-through.

Step four: Directly annex By now, the populace should be used to the taxes. While you wait for that to happen, slowly show more and more of your strength. Ideally this would look organic, like you're a fledgling empire yourself and growing. Then you and the local faction can do something like a corporate merger that, like many corporate mergers, turns into a buy-out. You can demand more money for defense agreements and have your faction hand it off to you, then at some point the politicians in your pocket decide it's more efficient to pay the tax to your empire directly. Now you have them by the neck, and hopefully the civilians welcome you with open arms, probably in spite of them complaining about the taxes.


In movies there's always an hero killing the bad guy (you?), I'd start by killing the hero. The rest should be trivial. And remember to kill him. No prison, as he would escape. Don't let him escape, as he would return. Just kill him when you can and don't start long monologues with the only purpose to give his friends the time to save him. Just please.


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