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What do space empires fight over?


Dying in Chargen
Three Body Problem's "The Dark Forest Theory" from the Second of the Trilogy by Cixin Liu:

The Dark Forest Theory was explained by Luo Ji as the implications of why Ye Wenji’s actions resulted in the Earth and the Trisolarans’ battle. This is due to two axioms: each civilization seeks to survive, and resources are infinite. He compares the universe to a dark forest: when two predators are aware of each other’s presence in the forest, they aren’t sure if the other plans to harm them. Because of this, it is inevitable that these predators will try to destroy the other and evade any other predators before they pose a threat.

Sometimes this is also called the superpredator answer to the Fermi Paradox.

Revelation Space also has the Wolves or Inhibitors who have a more sublime reasoning, basically destroying star faring civilizations to save life in the coming galactic collision between the Milky Way and Andromeda.

There is also the Culture-Idiran War in Banks Culture series, where the Idirans were on a sort of holy war against the Culture Minds and AI in general.

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Ancient artifacts, like in The Expanse. Things of power left by an ancient civilization.
This was going to be my answer. Lien tech able to do things the rest of the universes high tech cannot. Maybe even magic?

On a different note, one of my favorite sci-fi spacewar settings is the Star Control series of games. In the first Star Control, Earth joins an Alliance of Free Stars fighting against the Ur-Quan and their battle thralls. The Earth loses.

In Star Control 2, you return to Earth after being stranded on a planet where you find a Precursor starship factory. This alien super awesome ship takes you back home where you find Earth has been enclosed in an impenetrable shield.

Upon researching you find that the Ur-Quan offer the victims of their conquest two choices. Join them as battle thralls or remain trapped on your planet forever trapped under a shield. Further investigation uncovers an even worse species of alien, the Kohr-Ah, who go through the galaxy just killing everyone.

Eventually the two are going to meet in the center of knownspace and have a ritual dual to the death to possess a discovered Precursor battleship (your awesome ship turns out to the the equivalent of a tugboat).

The plot goes into the origin of the two species, how they both evolved from an original form, and why they pursue subjugating the galaxy in their own way. The story is reminiscent of the origin of the Gith in D&D.

To sum up: The galaxy is a mess because two of superpower factions are headed to war and everyone else gets swept up in their wake.

How about: there is no reason.

Scenario 1. Two major sides have been in conflict for so long that they literally have no history of what started the war. Communication between the sides was effectively destroyed (or never existed), so no political resolution is possible. There are mostly just small border skirmishes, but occasionally these flare up into larger battles. Both sides blame the other as being an aggressor, but it's really just a cycle of retaliation that has never ended.

Scenario 2. The leaders of each faction (however many sides you need) don't actually hate each other. But each one has a reason why war is useful. For one, it may be a political tool to keep them in power. For another, it gives motivation for technological advances. For another, it's a way to cull excess population of an unwanted sub-race. For whatever reasons, all of these leaders have an agreement to continue the conflict in such a way that none of the empires are actually at risk of losing and/or winning. Everyone at the top level has a way to benefit from the wars, and no one wants to change it. Of course, the rest of the population doesn't know this (especially those that die for they cause).


Staff member
Whether one empire can graze and water their space cows* where another might object.

I mean, sure, politics, religion, xenophobia and all that stuff all contribute their share, but an empire is an ever-hungry beast, and it must feed to grow or it will die out (eventually). So resource access- commodities, tech, or even habitable planets** - is going to be the big driver. And the dogmas may well be used for hunting them out.***

* or giant space hamsters.

** which wiLL differ from species to species, sometimes radically

*** yes, “hunting dogmas” was intentional

Or you could go the Babylon 5 route: A power grab occurs after the ruler of a nation is assasinated. The new ruler is a vile dictator, and his power grab fractures the nation, causing groups within to turn against him. Civil war on a galactic scale breaks out, and other nations are forced to pick sides.

Or shadowy organisations are responsible for the creation of a conflict that destroys the fragile peace between nations, causing them all to point fingers at each other.

Or a calamity on an epic scale occurs. All of a sudden it is every nation for them selves.

Or a hostile race appears with powerful tech. Several nations ally with them, while others turn against them.
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Power. Why did Alexander build an empire? Why did the Romans? Because they could. Empires were built because the people in it saw an opportunity to amass wealth and power. Not just the emperor but the average person. Everyone from the highest to the lowest used the empire for personal gain.


  • "There's no bottleneck or single-source resource" is not the same as lack of competition for resources that aren't quite common. Or even not the resource as such, but accessibility and prices of the resource and its derivatives. (cough see also: certain black liquid rich in hydrocarbons cough)
  • "Useful territory is not scarce currently or in near future" is not the same as lack of desire to defend one's already claimed territory. This opens paths to both conflict of interest and escalation, especially if the border is not straight nor backed by a long tradition, "safe" distance is great and the neighbor over there is not all that trustworthy in one's opinion.
  • Even if everyone involved is on talking terms enough to trade, there are many reasons someone may want to open or close a certain market, someone else may object… (see also: Opium Wars)


Technology could be a potential motivator. Imagine a larger empire that has historically grown more swiftly, versus a smaller empire that has recently developed new technology (faster FTL travel, or revolutionary new terraforming tech, or batch-cloning of populations) that is going to let it start expanding much more swiftly going forwards.

The larger empire may fear becoming overshadowed and consequently losing influence, or even finding themselves locked into their existing territory as the smaller one blooms past and around them, especially if the technology is something they either can't easily replicate or are unwilling to use.


Well, that was fun
Staff member
Or you could go the Babylon 5 route: A power grab occurs after the ruler of a nation is assasinated. The new ruler is a vile dictator, and his power grab fractures the nation, causing groups within to turn against him. Civil war on a galactic scale breaks out, and other nations are forced to pick sides.
Game of Thrones!


If there are no pressing territorial reasons for conflict, then that takes out an awful lot of possibilities. Historically religious and dogmatic reasons for conflict were little more than trumped-up excuses for either political or territorial reasons. Have a bunch of nobles that you think might cause you political unrest? Time for a Crusade! send them off to The Holy Land. Want to annex a neighbouring state? They're keeping us from reuniting with our traditional brothers!

You can go the religious route, but then you have to support it with pure dogma. From Here 'Til Underverse Come!

You can go the ancient technology route, but that's just substituting what your "scarce commodity' is. I used this in an old Space Opera RPG campaign, pre-Babylon 5 by a decade or more. A trope is still a trope, even when you change the window dressing.

There is something that you can do with tech, however. Different species aren't necessarily going to develop a given tech at the same time. Conflict could arise if one species withholds effective tech from another. More efficient drives that reduce fuel use. Better oxygen or waste recycling tech. Artificial gravity. You can't go too far, though, or any conflict would be over in seconds. The Minbari easily rolled up any human defence right up to the Sol system, barely breaking a sweat. If drives and weapons are TOO much out of scale then it's tough to maintain the conflict, unless the more advanced race is pacifistic to a fault.

Edited for crappy spelling
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Boredom. One society has become so advanced that everyone is basically immortal, with instantaneous memory backup and rapid cloning. Material losses are irrelevant and even death is only a minor inconvenience. After a few thousand years of this, people got so desensitized to this that to them war is just a break from the routine, regardless of whether this is true for the other side.

Or maybe a young generation is fed up by their stale/codified/ritualistic society and war is seen as a return to a nobler/purer/truest past, even to the point of rejecting immortality technology and looking for true death in battle.


There are aliens in the book First Contract that hate Limited liability corporations. As good as any reason to go to war.

Other reasons in no particular order
1. To Unite a single race (2nd Empire of Man - Pournelle and Niven CoDominium - Wikipedia)
2. To Unite all sentient beings (Star Wars Empire ??)
3. For religion (Ori from Stargate)
4. For ancient artifacts (Startide Rising - Brin )
5. Philosophical / Cultural Differences (Use of Weapons - Banks)
6. Misunderstandings (careful not to get eaten by a small dog) A quote from The Hitchhiker's Guide to the Galaxy
7. Revenge (Last Angel series The Last Angel)
8. unique resource Dune
9. Because you can just fight (Klingons - The Final Reflection indicates Klingons believe an empire is either growing or dying. There is no way to be static)
10. extermination of all life (Berserker series - Saberhagen Berserker (novel series) - Wikipedia


6. Misunderstandings (careful not to get eaten by a small dog) A quote from The Hitchhiker's Guide to the Galaxy
That reminds me of the Timothy Zahn series (I think I only read the first novel) about an alien species who were particularly vulnerable to radio waves. An unlikely scenario, but it does make for a compelling misunderstanding - from their point of view, the first thing any human vessel does when they show up is to shoot at them.

That reminds me of the Timothy Zahn series (I think I only read the first novel) about an alien species who were particularly vulnerable to radio waves. An unlikely scenario, but it does make for a compelling misunderstanding - from their point of view, the first thing any human vessel does when they show up is to shoot at them.
IIRC, the Oswaft from the old school EU Lando Calrissian Adventures had an inverse of this. They were a space-borne race that talked with some sort of high powered electromagnetic emissions. The first time the encountered a small ship, they tried to talk to it. It didn't respond, so they yelled at it. Then it exploded. Oops.


Guide of Modos
Because one space emperor had an affair with the other space emperor's wife.

To echo those who said it before me (you know, in the brilliant posts that I didn't read because they were too long):
1984. Constant war keeps the economy moving and keeps the proles distracted. They say they're fighting for victory, but the governments are actually just fighting to maintain power over their people.

I recall in the book Accelerando, there was a species of aliens that basically ran 'Nigerian Prince' scams on civilizations that were newly entering into interstellar exploration. In a universe without faster than light travel, it would offer an exchange of its technology for the cultural and artistic creations of the new civilization. You send us your copyrighted material, and we'll send you patents so you can build a hyperspace gate! Sure, it might take a few decades for the messages to travel at light speed, but once you get the hyperspace gate built, we can meet in person and trade real goods.

Except, lol, hyperspace gates are impossible. So dumb species send a bunch of valuable intellectual property and in return get some useless patents for superscience like fusion and antimatter reactors that, sure, might improve their standard of living a bit, but are old news among the interstellar community. Then the aliens get to score big by licensing all our pop culture.


Whatever you do, please, for the love of Roddenberry, do not put a population size under a billion on a planet and have them bitch about not having room to share. I swear, if I came to resettle a population whose planet exploded and got that answer from the existing colonists, I'd wipe every last one of those entitled whiners and make it the refugees new home world.


This is a world building question. What’s the conflict?

So if you have a galaxy full of space empires. Say a dozen at least, each covering a big swathe of the galaxy. And you assume that:

1) space/habitable places isn’t an issue. Space is big and they’re not short of land.
2) a single resource like Dune’s spice or Discovery’s dilithium is a well-mined trope you want to avoid.
3) you want to steer clear of “species” othering: assume they’re all human and have similar motives.

How do you create constant conflict between these space empires? If indeed you can after ruling out the above?

There might be a lot of land but how much is habitable? There might be plenty of planets but if you are going with all humans that implies complex life isn't necessarily out there in space. How many have a biologicals on them suitable to grow crops? If you look at the Expanse the Belters and Mars were initially tied to Earth because it was the only source of organics, you can't grow something without fertile soil.

Control of ancient jump gates to gain access to planets. Resource rich planets, asteroid belts, stars. Access to ancient technology,

Rather than species othering, culture othering, again The Expanse is a good example, they are all human, but try to take advantage of each other. Religion, politics, philosophy, ethnicity is just an obvious external difference, the USA and USSR never got on despite both fighting the Nazis and all of those countries were predominately white. Old treaties (like what lead to WWI) that pull nations in that otherwise wouldn't be involved, the need to be the dominant empire, the need to gain independence from an empire...

An enigmatic (but real) super-race who offers unimaginable wealth and power to the civilization who proves itself worthy.

Of course, what they mean by "worthy" is not something any two races agree on.

And at least a few of them think it must mean "ascendant in conquest".

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