# What could be a probable reason for an alien race to want to non-violently annex Earth?

An alien race suddenly appears and immediately declares that their intention is to conquer Earth. However, they are surprisingly amicable about it - they arrive, make known their intentions, maybe meet with high ranking politicians from various countries. They give us time to prepare, but either imply or outright show that we cannot fight them - their technology is far superior to our own.

What is a probable reason an alien race would want to begin (and presumably end) diplomatic relations like this? My own internal answer at this point is that the aliens are in an "Alpha Island" society, similar to Brave New World, where everyone is high class and they need us to serve as the lower class. However, I feel like this may be a weak justification for the strange proceedings.

The scope of this question mainly deals with the why - other factors such as Earth's response (futile war à la Independence Day probably) and other social factors may be asked in later questions. For this question, you may assume

• The aliens arrive over populated cities in the near future, with maybe a hundred or so ships.
• They have perfect knowledge of local languages, so communication is not a problem.
• Along with the previous, aliens try to meet with the every-man - they may even go door to door in suburban neighborhoods.
• My current idea is for Earth to be human-less once the aliens leave, but this point is undecided.
• Alien weaponry has not been demonstrated yet, but has immense destructive capabilities - a war would be ended quickly.
• The aliens would prefer to avoid bloodshed, but will cause as much as necessary until their goals are realized.

So, what goals might these extremely polite conquerors have?

• HI, user3656992, welcome to Worldbuilding. This sounds a little like Idea Generation to me, though other folks may show me wrong. – HDE 226868 Jul 13 '15 at 19:47
• Or use us for some insidious purpose, like in Arthur C. Clarke's Childhood's End. – drunkBrain Jul 13 '15 at 20:28
• Sorry, but get your ideas right. "Surrender or we will kill all of you" is not non-violent... If things were that way, a man that demands your money while pointing a gun towards you would not become a criminal unless he did actually shot at you (if he does not shot at you, the guy is just "non-violently" asking you for some money and you are "voluntarily" agreeing to his request). – SJuan76 Jul 13 '15 at 21:48
• But isn't it obvious? The only thing Earth has that you cannot get on any other planet are the beautiful fjords designed by prize-winning geo-designer Slartibartfast! – Burki Jul 14 '15 at 7:19
• Have you read Childhood's End by Arthur C. Clarke? I've seen ads for an upcoming TV movie based on it. – JDługosz Jul 14 '15 at 7:54

1. Annexation can be defensive in nature. Alien race A may know of an impending invasion from alien race B, and are attempting to annex Earth to protect it. Alien race B is out to conquer new worlds but knows that if it attacks part of alien race A's empire, a large-scale war would break out and race B would suffer greatly. Annexation by race A would serve to protect Earth against race B's aggression. Race A may be doing this altruistically, or may simply be trying to prevent race B from expanding (race B wouldn't want Earth if its inhabitants were killed off, so the violent route wouldn't accomplish the goal here).

2. The alien race may need the planet for something critical to their survival, but only after they arrive they notice that the planet is inhabited - possibly because our civilization is too "primitive" for them to notice from afar. It's too late to change their plans, but they're not willing to exterminate the native life unless provoked and with no other options. Perhaps they were forced to do this in the past and the memories of it still haunt them. The aliens' needs won't impact the native life forms at all (perhaps they merely need to set up a communication/transportation waypoint on the moon). They simply need the natives to leave their stuff alone and go about their normal business. The aliens quickly discover that the natives are unfathomably curious and will relentlessly investigate anything that they don't understand. The only way they see to ensure the project is a success is to take control and set up enough of an enforcement structure to protect their interests.

3. Earth could have some resource that the aliens desperately need. Approaching the situation diplomatically and gaining the cooperation of the locals would give them access to the resource relatively quickly. Fighting off the humans would also work, but would add a significant delay that the aliens can't afford. Avoiding a possibly-lengthy war and being able to take advantage of the humans' existing knowledge of resource X makes the "peaceful" route the more appealing path for all involved.

4. The aliens are bluffing. They could be overestimating their own capabilities (their fleet is actually heavily damaged and only a few of their weapons are actually usable) knowing that they're beyond the humans' level of technological understanding. Another possibility is that they've seen enough human activity - and possibly media - to know that they'll do desperate things in order to survive, and that some of those desperate things would actually be effective. Avoiding a war is the only real option for the aliens, so they attempt to politely intimidate the humans into submission until they can rebuild their fleet.

5. The aliens may be annexing Earth for economic reasons. As a colony of their empire, they would be able to collect tax revenue from Earth. In order for this to be profitable, they need to keep Earth's civilization, industry, and infrastructure intact. A war of subjugation would destroy their revenue sources and make the whole thing a net loss.

• I think the defensive reason is by far the best. – Loren Pechtel Jul 14 '15 at 2:28
• Selected as answer because it offers valid solutions less based on alien morals and culture, particularly 1,3, and 5. However, due to Philipp's and Thucydides' great answers I'm realizing that culture must play a large role as humans would be so insignificant to a race this powerful. – user3656992 Jul 14 '15 at 13:12
• In support of #4 "desperate people do desperate things"- the aliens may be set on avoiding any use of nuclear weapons. The radiation could be extremely harmful to them (more so than even to humans), or it could spoil the resource they are after. – fotijr Jul 14 '15 at 16:56
• The "defensive reason" has been explored quite a bit in Crest of the Stars. – Simon Richter Jul 15 '15 at 12:49
• I like the defensive reason. However, the ideas about aliens wanting resources must be implemented carefully. Raw materials can be found in space or made far easier/cheaper then traveling to new worlds, so one needs to be careful when describing resources. If it's to take resources home with them biological samples are the most likely, as earth is home to the only mammals, and not much else is unique about us. They may simply prefer a planet similar to ours and want to create a base or living location on an M class world... – dsollen Jul 15 '15 at 21:18

Keep in mind that an alien civilization might have a concept of ethics and morals which is completely different from ours and completely incomprehensible from our perspective.

They might have evolved into a centralized, non-violent hierarchy millennia before they even developed technology. A decentralized system with independent countries and organization which do as they please might appear immoral and barbaric to them. They might consider it their moral duty to bring order to our backward world by making it a part of The Empire. Denying us the joy of being part of their hierarchy would be unjust and cruel. It would be morally wrong to them not to conquer us. We humans might think that we don't want that, but that's just those libertarian demons who poison our weak, primitive minds. Our miserable lives full of conflict, rivalry and power struggle will improve so much after a few generations of intensive reconditioning.

Or when you find that too hard to write and want their psychology to be closer to the human, it could just be galactic-political interest. They could be competing with other spacefaring species in a race for colonizing any less developed sentient species, just like the colonialism practiced from the 16th century onward on Earth by the European superpowers.

Look up how countries like England, Spain and France "colonized" indigenous tribes in the Americas, Africa and Asia. Their modus operandi was very similar to what you describe. Appearing with demonstration of power and superiority but no obvious violence, gaining a foothold, extending influence over the local population and finally enslaving them, preferably avoiding wasteful bloodshed but not refraining from violence when deemed necessary.

• "They might consider it their moral duty to bring order to our backward world by making it a part of The Empire. Denying us the joy of being part of their hierarchy would be unjust and cruel." This reminds me of the Bush-era USA trying to bring democracy to Middle East and the colonial-era Britain trying to civilize the foreign "savages". – CircleSquared Jul 8 '16 at 1:37
• Don't forget that the English took Claim to Aussie-alia too. But I guess they count as Asian country, not sure how though; but on the bright side, at least the Socceroos get to be the best team in "some" region, think of how Tahiti must feel... – Harry David Oct 11 '16 at 11:03
• I think there is a deep mistake here by folks attempting to attribute a single motive to the aliens. Or to the humans for that matter. Read some good histories of the British Empire in India and you will see how complex and multilayered things actually were. In fact it might be easier to dress up parts of that history in C22 costume, than to write believable fiction from scratch! – nigel222 Oct 11 '16 at 19:49

Most of the answers, and indeed the implications raised in your question would seem to make this a non starter.

Labour? An alien race which can build starships and cross interstellar space can use energy and resources on a scale that is literally unimaginable to most modern day earthlings. It would be much like a wealthy Arab sheik deciding that he will create an even crazier set of offshore islands to compete with Dubi by enslaving millions of people and giving them shovels and pails to do the work.

Resources? There is more water under the ice of Europa than in all the oceans of Earth, and that is only one moon. They can scoop up asteroids, moons, strip mining gas giants and even surround the Sun with solar energy collectors to get all the resources they want, and at our current level of technology there is nothing we could do. They would not even need to talk to anyone or say please...

Living space? There are an estimated 60 billion planets in the habitable zone around red dwarf stars in the Milky Way galaxy alone: almost ten planets for every living human being today, if we could only get there.

So the reason needs to be something else. Alien philosophy or religion makes the most compelling reason (look up "Blue and Orange" morality on TV Tropes, for example). The reasons may be entirely incomprehensible to human beings, but perfectly sensible for the aliens. Their explanations make no sense to us, so as a writer you are even allowed a handwave for this.

The only other reason that I would consider is they are harvesting "brainpower". Two examples in fiction are "Childhood's End" by Arthur C Clarke, and the backstory of the Orion's Arm website.

In Childhood's End, humanity has some sort of "x" factor the Overlords lack; their job is to simply watch over us until the Galactic consciousness can come along to harvest us. The Galactic consciousness will be rather displeased if we self destruct before the human consciousness becomes "ripe", so the Aliens are there to make sure nothing bad happens to us.

In Orion's Arm, it is implied that the mass of S<1 baseline humanity is there for some sort of incomprehensible "ecological" reason to support the ascending levels of sapiences. Perhaps the collective trillions of brains are used as a sort of substrate to support the next level of sapience. When you are having a dream, it perhaps means your unused neurons are being accessed like the spare processor cycles on your computer can be accessed over the internet with the right programming (or maliciously via a botnet infection of your machine).

So let your imagination run away with you; just stay away from the various "old" tropes which make no real sense with the knowledge of modern cosmology.

• I've seen the "resource rejection" explanation several times now but still haven't seen any real explanation. It doesn't matter if there's more water in Europa than Earth. Sooner or later, the harvested water will run out. What you need is a rate...kinda like us and petroleum. Earth is simply next in their exploration and harvesting efforts. – DrZ214 Jul 15 '15 at 3:05
• @DrZ214 It won't run out, it's recyclable. Even if it did run out the resources on earth are such a tiny fraction of that in the rest of the solar system (let alone the galaxy) that it just wouldn't be worth fighting us for it unless everything else was cleaned out first. – Tim B Jul 15 '15 at 15:55
• The main reason is that it is very difficult to lift those resources out of Earth's gravity well. Those moons & rings of Saturn not only have more water than the Earth, all of it is easily moved to where you need it. If you are already in space, any material resource can be found & exploited more easily in space than on Earth. – Jim2B May 11 '16 at 19:56
• Re resources: You're forgetting your organic chemistry. There are a lot of complicated compounds which may be too difficult to synthesize without a carbon-based biosphere. If the aliens are non-carbon-based (or they're carbon-based with the wrong chirality), they might conceivably not have a better way to get those compounds than taking over somebody else's planet. Life is also conveniently fragile so the aliens can't just drop asteroids all over the place to get rid of all the humans. – Kevin Feb 8 '17 at 6:32
• @DrZ214 if you have used up (how?) all the water in the Orion arm, how long is the tiny bit of water on Earth gonna last you exactly? You can actually make water by combining hydrogen and oxygen, you know. So a civilization so advanced that they can travel to the stars is unable to put some hydrogen and oxygen into the same container and let them react? Hydrogen being the most abundant element in the universe by far, if you have "run out of" hydrogen, you probably have bigger problems than finding water. – Solanacea Mar 30 '17 at 22:47

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There are a few open spots in the question, so I'll take some liberties here, to justify why the aliens want to non-violently annex Earth. As an urban planner, I will apply the same reasoning we do here, but on a galactic scale; as well as more insidious reasons.

Labor

Compared to other planets that may just have bacteria, Earth has a large supply supply of inexpensive and (relatively) highly educated labor. The aliens ensure humans are fed, 'paid' and housed, and in turn the humans produce their products from service to labor employment. Think Abu Dhabi: paying expatriate workers more than they would get back home, providing free healthcare, education, and housing; and the people are complacent.

Resources

There may be a resource aliens would like to sustainably harvest... trees? They like the taste of wood (replace this with whatever resource is unique to Earth). They offer to help leaders keep their place, and people to be provided with nice things, so long as we sustainably work in the lumber industry (as an example).

Right of Way

There may be a reason the Earth is an un-owned piece of land that would make a nice traffic or utility easement (a stop-over or temporary accommodation), and before aliens #2 claim Earth, aliens #1 would like to annex the land and plant their flag, so-to-speak.

Organization

Maybe the aliens truly consider us a 'proper' civilization and biome (how flattering), and would like to formally include us among their amalgamation of civilizations. They're ready to include us as one of the 'territories' or 'states' of their societies, and allow us to join in the inter-galactic dialogue with them and others.

(My favorite) Investment

The aliens see us as potentially helpful, so they are ready to invest in the infrastructure, technology, etc. of Earth, in exchange for a growing security and resource provider: another ally. This is not unlike the EU Association Agreements with countries: we build ports, utilities and other infrastructure, in exchange for cooperation, investment opportunities, etc.

(for fun) Hotties

You're only allowed to date someone in your own interplanetary system; and they find us attractive, but until we're part of their system...

From a hard science perspective, there is very little that's available on Earth that they could not get cheaper and easier from somewhere else. Invading Earth for water, food, minerals, mates, or just about anything else is stupid, ludicrous, or crazy.

What they might find on Earth that could be rare in the Universe (and therefore worth the cost of invasion) is:

## Life

Earth has a unique biosphere which originated here based upon all the evidence we can find. It is likely (but not certain) to be different from life elsewhere in the Universe.

An alien civilization may want the treasure trove of biology found here on Earth or just not like how we're doing as caretakers of that treasure trove.

## Sapience

This one is more difficult. Members of other species possess some traits of sapience that we generally assume are unique to humans (some dogs show self-awareness, many animals use tools, Octopi learned out to open mason jars on their own, etc.). So alien life may view human levels of intelligence a very valuable commodity and may view our own self-destructive tendencies as ample reason to take over administration of this planet - peacefully if possible, forcefully if necessary (see Arthur C. Clarke's Childhood's End).

Perhaps they want us to serve as slave soldiers in their military forces. Or work in environments that are dangerous to them (they might also be dangerous to us but they don't have to be).

## Industrialization

You're an alien invader in a war of survival against a deadly foe. Your own productive capacity is pushed to its limit. Luckily, you found a backwater planet in an isolated place in space with 7 billion people and lots of excess capacity to produce your war fighting materials.

There's just the simple matter of quickly and unequivocally convincing them to turn that productive capacity to your needs.

If intelligence is rare, then an industrialized society is even rarer. The alien's could produce things more efficiently than we could. It might be like our modern society utilizing the manufacturing output from the 1600s. It'd be crude and the quantities wouldn't be very impressive compared to what we can do now, but that extra 1% added to the war effort might be just what Xog the Emperor needs to win. Plus with some key advancements they might increase the quantities and improve the quality of output.

Just be wary of those duplicitous humans, who simply don't understand all that Xog has done for them.

## Intellectual Property

Art, music, architecture, engineering, science, history, etc. Aliens mine the databases of other races and use the information for advancing themselves. They may have stolen star drives from another race and simply don't have the background to understand what it is that they have. They raid or conquer other races to collect yet more technology and information.

Or pirate music mp3s for selling on the galactic market.

Human understanding of physics and engineering might be woefully inadequate on the Galactic stage, but perhaps Humans are the Galaxy's experts at spinning entertaining stories or writing computer viruses.

Still most intellectual property can be far more easily transmitted to other places, so it's usually better to trade for this than to attempt to capture it.

1. Upvotes. Badges. Karma. Thumbs up. Appendages up.

Basically, the aliens need to incorporate Earth into their sphere of control to gain social networking points and keep their rivals from claiming those points instead. First alien civilization to gain 100 "planet points" gets a gold badge. Basically, this is planetary-conquest.stackexchange.com

1. Uplift.

In David Brin's Uplift War science fiction series, there is a lot of value in species that are on the brink of intelligence on an evolutionary scale. Dolphins, Chimpanzees, etc. have potential for sentience and claiming them as client species is valuable to the alien civilization as a whole. Claiming Earth as a client planet would give the alien civilization access to the genetic diversity of this planet. Keeping humans in line is important to ensure we don't drive any potentially valuable species to extinction.

• There's both a prestige aspect and a practical aspect. Races that have uplifted many other races are considered more prestigious (this is a sort of social prestige). There is also a practical power aspect since a race that has uplifted more races has a larger and more diversified racial "clan" with which it can dominate others. – Jim2B May 11 '16 at 20:05

I can't believe no-one's mentioned Star Trek yet. Some key technology may exist whose invention can be detected by the aliens (warp drive, for Star Trek). The question then is why alien intervention might be required, and I can see three basic options.

The tech may have the potential to kill the Earth, and without the right theoretical backing it might be unclear to noobs how to control it, or even that there is a risk at all. This would be the aliens altruistically intervening to keep us safe until we have the knowledge and cultural sophistication to not destroy ourselves.

If properly exploiting this tech would put us on an equal footing with the aliens (or possibly better; consider reproductive rates), there's a real risk that we could try for an invasion if it looks like we could win. If the aliens are working on the basis of enlightened self-interest, they could be keeping a lid on our society until they're sure we're grown up enough to not do this. (Currently it's pretty clear we aren't!) So like any grown-up supervising the kiddies, they're keeping us away from the sharp knives until we can be relied on not to stab anyone. This is basically the "The day the Earth stood still" scenario - we're required to keep the peace and threatened with overwhelming force if we misbehave, not because it's the right thing to do, but because it's the only thing that actually works.

And the third option stems from the above, but doesn't assume such goodwill from the aliens. They might not want to kill us (yet...) but they would at least want to take this tech away from us so that we're not a threat to them.

It would be considered rude

It could be important to differentiate "friendly" or "non-violent" from "obeying the Space UN." While it might be acceptable for them to colonize or take over our planet in the broader intergalactic community the wholesale slaughter of a species that doesn't even have particle weapons or "at will" space flight might be considered somewhat gauche.

We as a species have no problems extracting resources from tribal lands but it would another matter entirely if we killed all the natives first (at least recently, in the past this was also deemed acceptable).

TL;DR - The Naval Expeditionary Force that arrives might have no qualms with destroying us and might in fact prefer it however the Intergalactic Council for the Development of Infant Species/the Lib Arts students back home might have another view on the eradication of an undeveloped native species.

Alien weaponry has not been demonstrated yet, but has immense destructive capabilities - a war would be ended quickly.

The war might be end quickly, but that doesn't mean they wouldn't take loses. Along with the other reasons that have been mentioned, perhaps they have few defences against nuclear attacks. Or maybe it's just a cost issue, diplomacy is cheaper for them than war. They could take over the planet with force if they needed to, but they don't want to put out an alien bond issue to pay for it.

Because we are their 'Creations'.

When the aliens chose the earth (and most likely many other planets) to colonise, they first sent out a fast bullet-craft to begin terraforming the planet. A small craft containing non-organic nanobots should be able to accelerate and decelerate much faster allowing them to arrive much earlier than a slower manned craft; It would also be able to be deployed more easily and therefore earlier then a fully manned mission, similar to the mars rover which is already on mars and yet a manned mission is still many years away. The nanobots just kick start things and push them in the direction needed to change the planet to be more suitable for the host. Sometimes sometimes when doing this intelligent life evolves on the target planet and it is customary not to kill them; however they are your creation so there is no reason they should be allowed interfere with the original plans laid out billions of years before...

Humans are somewhere between farmyard animals and unruly children.

• Hi, welcome to WorldBuilding SE; I like the answer, but I'd suggest elaborating more on this "Bullet craft" you've touched on, seeing as it is some of the main reasoning behind your answer :) – Harry David Oct 11 '16 at 8:36
• Well I didn't think this needed much explanation... most organic beings have a limit on their tolerance to acceleration, a smaller ship without complex organic beings on it should be able to be accelerated (and decelerate) much faster. As a result it should be able to arrive at the destination a long time before the main fleet. All it would need in it's cargo is some nano bots sufficient to kick start the planet and possibly guide it through various stages. Sometimes this process might be too successful and produce intelligent life leading to the current dilemma. – tarriel Oct 11 '16 at 12:50
• Thats a great explanation! Add it into your answer and I can almost certainly guarantee you'll get a couple Up-Votes for it B) – Harry David Oct 11 '16 at 13:14
• I should also add that the 'bullet' ship could be deployed well before the main fleet, it should be a relatively low cost probe deployed without much fanfare. A species traveling to a interstellar distances at sub-light speed should not be too hasty to leave with a fully crewed ship. – tarriel Oct 11 '16 at 13:19
• Once again, a great point - generally the more relavent context you can add to an answer, the better it fairs. – Harry David Oct 11 '16 at 13:23

People are soylent green.

They simply want a continuous supply of humans who have died of old age. Maybe we do not taste that well if we have been killed prematurely, or there might be another purpose for which they need old dead humans.

They could offer as a condition for helping us evolve, that corpses would have to be sent to a facility they have established to be treated before burial (always closed casket, never actual contents).

Killing a lot of humans in a hostile take-over would reduce the world population and would reduce the output for generations.

1. Mistaken Identity – Humans either look a lot like a species they have had to wipe out in the past or possibly long lost colony or that species. Maybe it is a case of incorrect paperwork being filed.
2. It is a test – They want to see how we react to this threat, maybe to join them or just for science!
3. Proactive threat removal – Humans are a possible vector of a plague and it is effective to wipe them out proactively. Another twist would be they have projected that humans may become a threat in the future once we advance. How about our existence threatens them culturally in some way, either morally we might corrupt them, or if the general alien public knew life was “out there” it wouldn’t jive with their creationist religion.
4. Experiment is complete – Either they have completed their research and won the alien nobel prize and now they are cleaning up the petri dish called Earth or their funding was cut after showing no useful results (same outcome for us).
• I'm not sure that some of these count as nonviolent. – HDE 226868 Jul 14 '15 at 19:24

Let's start with the facts: -This alien race can travel across vast distances (interstellar) with ease. This means it already has access to and mastery of whatever material resources and energy it needs. So it isn't coming to Earth for them.

-We all know from science fiction series like Star Wars, Star Trek, Dr Who, Flash Gordon, Battlestar Galactica, Buck Rodgers, Aliens-Prometheus.... that humanoids are not that uncommon. However, unlike those series (which are not documentaries, or Ken Burns would be narrating) we know that, in fact, humanoids tend to be the least developed of "sentient" creatures in the galaxy. They typically annihilate themselves on reach technological levels comparable to our 19th-22nd century levels. Either through resource mismanagement, pollution, gaian collapse, nuclear war, disease, overpopulation... or frequently some combo thereof humanoid races tend to be erratic and transient. So they aren't here for our technology or insight.

-Sometimes we have areas that are culturally rich like Bali or India (here on Earth) but by in large we tend to be fairly uncreative, utilitarian, and dumpy in our cities, temples, and arts. So they aren't coming for the human cultural achievements like some space tourists.

There is, however, one resource on Earth that exists no where else in the universe which is beyond comparison- cats! Cats cannot be found on any other worlds, and moreover, cat videos can be used as a high denomination currency as well as a powerful balm to soothe the aches and pains of many a civilization.

The non-humanoid races that have developed and mastered interstellar space travel, cannot even hold cats or care for them easily (owing to incompatible biology, chemistry, temperature / pressure,... requirements). For instance, the Ol'tharg (which, to a legally blind person, might look slightly like a squid) live in a dense cold ocean of ammonia / amines and are about 300 meters tall (from the tip of the "head" to the end of the longest tentacle). They might find the odors from the litter-box to be soothing but they would have trouble holding a cat. Thus the aliens need to annex Earth and have us keep the cats (and keep making the cat videos) for them.

• We all know from science fiction series like Star Wars, Star Trek, Dr Who, Flash Gordon, Battlestar Galactica, Buck Rodgers, Aliens-Prometheus.... that humanoids are not that uncommon. They have to be prevalent for the purposes of these films. Humanoids are not necessarily not that uncommon. – HDE 226868 Jul 15 '15 at 21:53
• HDE 226868 these series are "science-fiction" meaning part science, part fiction. The science part is that humans are scattered about the galaxy. Everyone knows that the now extinct Ultharg scattered proto-human biomes (biological systems that would evolve humanoids) across the galaxy about 6 billion years ago. They planted them about as entertainment to other races in the area much like how our children take amusement in "sea monkeys". – Dan S Jul 15 '15 at 22:25
• Regarding the former, take Star Wars as an example. Not much science there. Regarding the latter, surely you're joking. – HDE 226868 Jul 15 '15 at 22:27
• Well, the science part of them is JUST that there are humanoids across the galaxy. You should really read Aadard Lemur's "Rise and Fall of the Milky Way". Written in middle kri-krell it can be a bit tedious like the 11,482 page introduction which is largely "thanks mom for giving birth to me"- but then he writes in rhiming couplets and only 1% of that language has rhiming words. I'd reprint it here but this comment section is too small for it. – Dan S Jul 15 '15 at 23:12
• The only other possibility would be that the aliens are completely centered on "practical jokes" (like the Umgah of "Star Control") thus they non-violently take us over and "enslave" our culture for 1,000 years because then (in a sense) that would make the Scientologists right. – Dan S Jul 15 '15 at 23:26

What if they simply want a collection of humans to show off? Perhaps unnecessary for any seemingly practical reason, it might fulfill some sort of psychological need. having exotic things to show off to others has been a human trait for a while. Certainly seems possible that intelligent aliens could want to do it as well.

It seems likely to me that this alien society is either moral in and of themselves or they're having morality imposed upon them by a more powerful force still. I see no other reason for an advanced species to keep such a comparatively primitive species such as ourselves around. If they weren't constrained by someone's mores against genocide, there would be no reason not to kill us all, and still less to tell us before invading.

Even if it's not "morality" exactly, well, it's surely got to be some social, rather than pragmatic, value. Like, maybe in their society it's considered a status symbol to collect as many planets, or even sentient species, as possible. Whoever dies with the most toys wins.

Or, just maybe, they're planning to set us up as a scapegoat.

As a highly advanced alien race, they have discovered that critical applications of their hybrid organic/AI technologies work exponentially better with human DNA than with their own planet's genetic materials. They need a lot of human DNA since their empire is vast. Thus, they have no intention of killing us. They want us to reproduce.

So why wouldn't they genetically engineer the necessary DNA? Lets just say that nature makes exactness impossible and that all attempts to produce synthetic human DNA quickly become unstable.

EDIT To be clear regarding genetic engineering. There is only one type of life on planet earth and all of our g.e. technologies use these genetic materials. We do no synthesize alien genetic materials.

• Why would need they to annex us? We have machine that duplicates chains of human DNA thousands of time, and with our currently genetic engineering we may put human DNA slices in bacteria if we want a more biological approach. A more advance race will probably be able to generate the DNA they want out of nothing. And, in the strange situation they are not able, they just need to kidnap some individuals and make them reproduce, without antagonizing the whole Earth. – SJuan76 Jul 14 '15 at 13:04
• @SJuan76 An individuals DNA is only good for about 80-100 years, tops. The mechanisms involved in its reproduction break down over time and one needs to return to the sperm and ovum to reboot the whole process. Regarding generating DNA out of nothing, please see my EDIT of yesterday. – Epsilon Jul 14 '15 at 14:32

I find it unlikely that there's any particular 'natural resource' or whatnot that the aliens would need. However, if such a scenario were true they might be attempting peaceful annexation because they would not only like to avoid the delay of a war, but also because the resource could be damaged by the complete devastation of the planet by a nuclear war. (Even at their level of technology, blocking thousands of missiles from going off in the event that humanity attacked them and they returned the volley could be difficult once the missiles were already in the air.)

Well, if i was an alien overlord, this would be my reasoning:

The Earth is a rare jewel teeming with biodiversity, natural wonders, and incredible unique species to be found nowhere else in the galaxy. Humans are f***ing it up. Somebody with more sense needs to step up and rein us in before we tip the whole thing into a catastrophic irreversible downward spiral.

• Not just Earth but every habitable planet would have its own unique evolutionary history producing unique forms of biodiversity. There is a cornucopia of pharmaceuticals and medicines still to be found in the wildernesses, both on land and in the sea, right here on Earth. For a galactic culture able to reach billions of planets this would be an incredible treasure trove. – a4android Jul 8 '16 at 6:49

## Safety!

In the book The Killing Star, the authors point out that any species capable of making a sublight interstellar ship is easily capable of killing its neighbors.

So as soon as Humans demonstrate the requisite technologies, the neighbors show up to force Humans to act responsibly.

1. Courtesy
As multiple answers have already touched on, the Solar System (as a whole) has far more of every local natural resource than the Earth, alone. There is very little sense in dragging materials out of Earth's gravity well when comets, asteroids, and moons can offer the same materials without so much gravitational opposition. Perhaps a neighboring alien race (or empire) has decided to annex the whole Solar System. Perhaps they thought it would be rude to start mining asteroids asteroids for metals or Europa for ice or skimming Jupiter for hydrogen without first informing the local tribes who will certainly notice all the goings on in their backyard. Perhaps they didn't notice us when they formed their plans or perhaps they didn't care. Either way, they may only go as far out of their way to accommodate a barely sapient species as we do when it comes to monkeys. Another thing this scenario has going for it is that they wouldn't technically be damaging our habitat. Lastly, there would literally be almost nothing (if not nothing) we could do about it. A far superior authority would simply inform us of their recent property acquisition (which includes us), and their activities would barely be within the reach of our most advanced probes.
2. Proselytization
Perhaps an alien race is motivated to annex backwaters for reasons similar to why missionaries, a millennia ago, traveled to foreign kingdoms. They could see it as their duty (burden, even) to civilize species smart enough to be instructed and molded. Given our backwards and unenlightened state, our desire to not be owned or dictated to could could be perceived by them similar to how we see children not wanting to eat vegetables. "You don't like it now, but give it time. When you're older, you'll be happy I didn't give you a choice."
3. Reasons unknown
The aliens in question may have reasons we can't understand or they may have no interest to fully decode how we think and communicate. Consequently, they may never interact with us more than whatever is enough to get us to do what they want. Similar to how we give auditory and visual commands to dogs (with whom we can't meaningfully communicate). Perhaps from our perspective, a group of beings which can dominate us simply decides to. They inform us of our current condition and simply pay little mind to our cultural disposition to bring annexed.

Sapience is rare in the universe. The aliens believe we are well and truly on the road to catastrophe, and they're saving us from our absolutely worst enemy, namely, ourselves.

Of course, there might be a sapient species nearby which believes in zapping first to remove any likely competitors. The sort of competitors likely to use relativistic, planet-killing weapons on their neighbours. A zap first or be zapped policy. The invaders are protecting us from the neighbourhood zapping thugs.

For the same reason that cities annex historic buildings: to gawk at how hideously they're built and yet still manage to survive.

GSP has already mentioned David Brin's "Uplift" universe. I'd like to add another possible reason based on that background: to protect the rest of Earth's ecosystem from us.

The alien civilization ("the Galactics") in the uplift books is on the whole very protective of planetary ecosystems, as they're the source of potential new client species, which can be uplifted to be new members of the civilization.

First contact with the Galatcics occurs away from Earth, on an exploratory starship, and they are able to warn Earth before the alien emissaries arrive, giving them time to cover up some of humanities worst offences (I think this is background info from the GURPS Uplift sourcebook, rather than any of the actual novels).

If humanity hadn't had this warning, then the aliens would have (after a long period of bureaucratic wrangling...) come in and taken control to protect us and the rest of the Terran ecosystem from us.

(More or less the same way we'd react if we found a 5 year-old looking after a baby)