A couple friends and I are currently doing a space adventure game similar to Starflight I & II, Star Control II, etc.

The Empire

The story involves a space-fairing Human Empire that was wiped out thousands of years before the game takes place. The Empire, as it was known, was the dominant power in the local region of space. All of the local alien races were either absorbed into the Empire or disarmed.

It should be noted that despite being called the Empire, this is not "The Empire". It is much closer to The Federation. In general, the Empire was benevolent and well respected by its citizens - both Human and alien. The only groups to really oppose the Empire at all were the races forced to disarm after refusing membership in the Empire, but even they don't have much issue with it; other than having their weapons taken away and being monitored for arms development, the Empire left them well enough alone.


The Empire existed as the dominant power for thousands of years, with it's heart centered around Sol and the Earth. Every member race had a voice in government through locally elected governors. Although the Emperor/Empress technically had final authority on all issues, they rarely intervened, preferring to let each nation/planet/system rule itself as fit, following a simple set of guidelines laid out for them.


In its current state, the game takes place in a 1000 x 1000 grid with a little over 900 star systems, and an average of five planets each. Of these, the Empire directly controlled around 200-300 stars at its height. Most of the other stars were ruled through their member races. The Empire was based roughly around the center of the game map on Earth.

The player's race, just getting into space and exploring, is located near one border of the Old Empire. The other races are on mostly on the far side of the Old Empire, and do not travel through that space due to its being "haunted". No one knows how Humanity got obliterated, and it's not worth risking wandering in there.


About 7000 years before the game takes place, the Empire was attacked without any warning by an alien race previously unseen in this region of the galaxy.

In a matter of weeks, the Empire crumbled as world after world was destroyed mercilessly. Despite having the best ships and crews available, the Royal Fleet was completely outgunned and suffered constant defeats. Thousands of Imperial ships were lost, with only a few alien vessels destroyed. When the aliens quickly made it to Earth, the Royal Fleet made one last stand and then helplessly watched the Earth get bombed.

During this time, only Humans were targeted. Initially some other member races tried to provide shelter to refugees, but the aliens almost immediately found these places and destroyed them. Following this, no one would accept Human refugees running from the carnage facing the Empire.


As quickly as they appeared, these unknown aliens departed. The entire Human race was wiped out, but all other local species were left (mostly) unscathed.

Thousands of years later, however, these aliens return. This is around the time the game starts, and is where we've drawn a blank. After such a massively overwhelming victory, why would a race just up and leave if they're planning to come back later to wipe out everyone?

I should point out here that this game, like many other works (Star Trek, for example), is meant to tell a Human tale. As such, we can assume that these aliens have Human motives. Let us also assume that it's not a result of something internal; they aren't fighting a civil war or anything.



closed as primarily opinion-based by Aify, Bellerophon, Slarty, Ash, sphennings Oct 23 '17 at 0:31

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Welcome to worldbuilding. We prefer to provide answers which can be objectively evaluated and not subject to opinion based metric. Your question seems to fall in the second category. Can you try to rephrase it? Else it may be closed. $\endgroup$ – L.Dutch - Reinstate Monica Oct 20 '17 at 6:46
  • $\begingroup$ I think this is a good question for here. I think you still have to clean it up a bit. Throw everything out that isn't related and tell us some constraints so that one doesn't have to waste time with an answer going in a completely different direction than you'd have liked. Btw not 100% sure I get the question, could you highlight it? "How does an extinct alien race return with their fleet?" Not sure $\endgroup$ – Raditz_35 Oct 20 '17 at 7:14
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    $\begingroup$ This is a standard trope and the list of potential reasons is as long as your arm with none really standing out from the others $\endgroup$ – Separatrix Oct 20 '17 at 7:22
  • $\begingroup$ Oh, come on. I've written a page long idea and then I discovered the question has been locked. What should I do with that now? ;) $\endgroup$ – makingthematrix Oct 20 '17 at 9:39
  • $\begingroup$ I've cleaned up the question and tried to make it more clear what exactly is being asked. Thanks for the help! $\endgroup$ – CaptainAdlai Oct 20 '17 at 21:33

Some ideas, mutually exclusive...

Read a book once which had a similar scenario. The destroying aliens were themselves refugees from another galaxy, driven out by some third group. So in an effort to "never get hurt again" the aliens sent massive fleets out ahead of their migration, extirpating all life that they could find. Centuries or millennia later they'd send another extinction fleet back along their path where resistance had been strongest, in case angry survivors had built up again. Since aliens were receding, the successive extinction fleets were coming at longer intervals, but they did keep coming.

Another thought is that your destroyer aliens underestimated the old empire. They sent in their fleet and destroyed the empire, but the defenders trashed them pretty hard before they went down, making the aliens believe they didn't have enough force to accomplish their goals in that part of the galaxy, so they retreated. They went back home, waited til they thought they were ready -- which is now -- and have come back, loaded for bear. (You'll need to explain why this part of the galaxy is so important to them, but hey)

Maybe the original alien fleet was a bunch of rebels or schismatics from the real alien empire. They destroyed the human empire (again, with hideous casualties) and have been living there happily for thousands of years. But the Home Office has finally tracked them down...

Could be there is just one planet or nebula the aliens wanted. It is aesthetically or religiously pleasing to them. They conquered it and an acceptable perimeter around it (the haunted zone). All they want is to be left alone. But all these weird ships have started poking around near their sacred space, so maybe they need to extend the perimeter so to speak.

The "alien return" is a coincidence. A completely different species has learned spaceflight and come to power in the haunted zone, wondering why all the nearby planets seem so ... glassy. They are understandably paranoid.

The Aliens have been lurking in the haunted zone for all these years. Turns out they are divided into two moieties; one believes in love, happiness, and isolation. The other believes in love, happiness, and the destruction of all non-them life. Every N thousand years (based on some astronomical events) they switch which group is in charge.

Another one from a book I read. The aliens worship certain energy beings which wander aimlessly through the galaxy, occasionally "resting" for a few k-years inside planets. The aliens follow the energy beings, destroying anyone who gets too close (to protect their gods, right). Well, resting is over, the energy beings are back on the move...

Oh, the list goes on. Could be the Emperor died, so the alien horde had to return home to elect a new Khan. Civil war followed, now they've recovered. And so on.

Good luck!

  • $\begingroup$ That first book you mentioned is "Empire from the ashes" by David Weber. (Actually a trilogy but later also published as a single volume.) It was my first thought too when I read this question. Very similar premise. $\endgroup$ – Tonny Oct 21 '17 at 7:55

I don't like much ideas turning around hostile aliens so powerful that the are able to destroy the whole interstellar civilization in a blink of an eye and then disappearing without a trace.

One of the possible explanations for such an outcome, and I think a bit more interesting, would be the massive use of biological weapons on both sides. Both humans and aliens infect the other side with plagues which are unstoppable and which wipe them out completely and this is how the war ends. But some remnants of the alien species survive on a distant planet. It takes them several thousands of years to rebuild their civilization and come back for revenge. In the process, the knowledge who were their enemies is lost, so when they find the ruins of the human civilization and another species in their viccinity, they assume these are humans and immediately attack. This scenario gives the player the possibility to win the game not by winning the war, but by convincing the aliens they are mistaken. To make the things morally simpler you can make it so the humans were really the bad guys here and the aliens were only defending themselves in that first war.

But that's boring. Let's have something else.

Consider mosquitos. They're active in a short interval of a year. In Lappland one day there are no mosquitos in the woods, the next one you're literally not able to walk through without being wrapped in a cloud of repellant. They hatch from eggs, go through a short larvae-pupae period, and then they transform into the adult form. As adults they try to find a source of food to have energy to mate and lay eggs. Then they die and the new generation awaits the next year.

No, I don't suggest the aliens to look or suck blood like mosquitos. I'm pointing to this repeating pattern of behaviour. A mindless predator killing their prey as quickly as possible in order to obtain resources for reproduction would be like a plague so deadly that it does not give itself time to spread. A species which want to use this pattern successfully on the interstellar scale has to be subtler and at least a bit intelligent. They may, for example, have their "larvae" period as harmless and quite intelligent beings. Once upon a time human explorers found a desolate planet full of ruins. They also found eggs (or something similar: I wouldn't like it to look too similar to the "Alien" franchise). They scanned them and decided they're pretty harmless so they took them home for further investigation. The eggs hatched and small, cute, intelligent creatures came to life. First they lived in the research centers, but since consecutive tests were showing they're harmless, and they were intelligent enough to be treated as chimps or dolphins, or even little children, it was decided that they should have be treated better than that. After all, maybe they're last survivors of an ancient civilization, who knows? The catch is, the transformation from the larvae into the adult form changes the creature completely, together with their brain functions, so the larvae may be genuinely friendly and harmless. Only when the period comes to end all of them very quickly transform into a much more deadly, carnivorous form. At that moment there were so many of them, and the security concerns so non-existent, that they were able to kill almost everyone in very short time. And having enough resources they were able to multiply quickly, without a period of being dormant. Only after they killed off all humans they turned against themselves: They killed each other for food and to lay eggs and the intervals between laying eggs and hatching became longer and longer. When the next species discovered the ruins of the human civilization, they also found millions of harmless eggs lying around and no living adult creature.

And this is how Gremlins came to be :)


The player activates a device he discovers. By accident of course or because someone thinks turning it on does something else. This device turns out to be a failed science experiment: more precisely a time machine.

As it turns out they did not vanish, they were transported into the present by the player. Now they are very angry at everyone for obvious reasons.

This doesn't have to happen over night or localized, a stepwise transport is possible.

Paradoxes? Well, it's time travel. One of the amazing things about it is that you can make weird stuff happen in a story and the illogical becomes logical.

Why was the machine working like that? If you are interested in the idea and can't think of anything, I might put my mind to it. But there are many possibilities. The most obvious one would be "they did something wrong when turning it on" or the aliens could've had some plan for it and were unlucky you turned it on with a date set the day before they wanted to use it. Classical time travel madness


The aliens are using a stardrive unknown to the races in your area. It permits travel over very great distances but can only be used when there is a suitable stellar configuration. (Perhaps a pair of neutron stars in exactly the right orbit to warp space appropriately to use the drive.) The aliens only show up when such a configuration exists on both ends so they can get here and also get home.


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