Well, I thought I'd take a stab at this, but since my understanding of the Xenocide world might be slightly off, I've posted it here, partly for discussion, partly to put everything in context for myself.
As Azrael said, we have some clues of the backstory (like the overmind ability to control other species and that), but we dont have an "Official" History about that... with those constrains you can write your backstory and we will choose later the one that fits the best for The Story of Xenocide Aliens.
Please Azrael, can your team write a simple list in the Wiki of the "Already known facts" about the aliens so everybody can write based on that. BTW I want to personally oversee it before publication.
- Aliens are mind-controlled by an Alien Overmind.
- The Aliens come from elsewhere through space-flight, an ability that has since been impaired/lost in some ideas. Possibly, the Overmind originated on Earth long, long ago (Bruenor's Ammonite Origins)
- The Overmind is currently based on Thanatos (on Mars, right?).
- The mind control is accomplished via brain implants (Alien Breeding) or colony implants (tzuchan's backstory). Perhaps both can be accomodated: the implant can be organic in nature, too.
- Humans can be mind-controlled in the same way if they are brainwashed/implanted (Alien Infiltration)
- The Overmind desires the subjugation of humanity, not its destruction. (Az's Alien Goal)
- The Aliens have a high degree of skill in bioengineering (many texts allude to genetic alteration of Aliens)
- The Aliens have a high degree of skill in technicals, though (imho) they do not seem to innovate, or cannot innovate as well as humans can. Perhaps the technology was stolen/assimilated. This might work well with the idea that "the Overmind wants humans as slaves due to their high potential" (Az's Alien Goal, Chmmr's backstory)
- Humans can only get/salvage Xenium from the Aliens.
- First recorded Alien activity (alien abductions) in 1961 (Az's Alien Goal, Alien Abduction)
- First UFO shot down in 2011 (Az's Alien Goal)
- Aliens attack in 2012, destroying satellite defenses and some major earth military installations (Az's Alien Goal)
Other working ideas
- The Overmind is colony-based (tzuchan's backstory) or an artificial brain (Chmmr's backstory)
- An explanation for why the Aliens don't attack at full strength and/or why they get stronger as the game progresses:
--- 1) Overmind has sustained from damage; it's mental functions are impaired, but resource gathering helps it recover it's full abilities (a post of mine in Az's Alien Goal, Facehugger's backstory)
--- 2) The Overmind presumably faces resource deficits as the game progresses, the stepped up attacks are a sign of desperation (Az's Alien Goal)
--- 3) The "Overmind" is the Ethereal race, wanting to supplement the Ethereal genome by assimilating other life (Deimos's backstory)
--- 4) The Overmind starts off with only the Greys and basic tech, it uses its bioengineering and science skills to develop increasingly advanced Alien strains and technologies (a post of mine in Chmmr's backstory)
- The Overmind is in a war against another Alien race, the Vaaish (tzuchans's backstory, Facehugger's backstory)
- Another Overmind (ship?), the Cthulu, lies dormant at the bottom of the Earth's oceans (tzuchan's backstory)
- The Overmind may be trying to wipe out humans to save the T'leth, aka the Atlanteans (Arky's posts in Ammonite Origins)
I'm sure there's plenty of ideas that I've missed. Help me!