suggestion:
---Artifact(s)---
A) It's was a ancient "mega-computer". Computer that missions was to store+analys+send foward info and orders (saves aliens brain cells from getting too much info and allowes them to live longer). By an accident (or someones will) computer started sending foward "kill'em" info that drived aliens grazy.
Grazy aliens are just attacking everything and are also looking for the master computer, who now controls them, Thats why they won't nuke earth. They don't know its location, only thing they know is that they need certain materials to dig out? (open or whatever) the Computers hiding place. All of them want to do it faster as someone else, and they have bloodlust. They work unorganized as computer can't control them so much yet
Some aliens who didn't use the super computer system, were not affected, they are the ones who're building bases and kidnaping humans (for finding out why humans attack them(normal humans don't know that).
But humans attack them cuz they think they are hostile. It takes some time (new thecs) to understand that (for humans).
Non hostile aliens don't want to kill theyr comarades who are under control, as they know that they can be saved. Do Win you must
A) destroy artifact - and non hostile aliens will be your enemy.
To win after that u must destroy one mothership (that is only remaining base of non-hostile aliens) <--- NORMAL ENDING
B) Get control over certain "keys" (sfinks, great wall, ancient atlantis remains, mystical artifacts - exmpl: Thor(Vikings god) hammer and Hermes(flying msg of zeus ((ancient greece)) boots). Then when u obdain certain number keys (aliens try to get them too) u can enter underground (mont blanc, mount everest, wherever) and charge into the computer room thats a 2-4 parts mission. Where u may not shoot computer (randomly on ground laying sircles or boxses) but must archive control of computer rooms.
First two parts would be full of normal aliens (hovernets and cyborgs, grazy atrealians (whatever theyr name was)) , last parts would be full of ancient and powerful self-defence cyborgs (even sectoids maybe).
<------- GOOD ENDING
C) Submit with grazy aliens and destroy everything (including earth pp, countryes won't fund u but UR BAD THEN)<--- BAD ENDING
Simpler graph of "master computer as artifact":
Artfiact - Alien mind controling computer.
Artifact Keys <-- needed for good ending (artifacts that humans know as items of gods)
-----PLOTS----
1) Good <- u take control of master computer, control the keys on earth and disable the mind control adn live peacfully (til next game)with aliens
2)Normal <- U destroy artifact (non-controled aliens will go in rage, controlled ones die or attack everything on earth and die then). Do win u need to destroy aliens last hideout (theyr mothership)
3) Bad <-- u join with mind controlled aliens, your mens go under computer controll, u have to destroy or kill as many humans as possible (conquring missile silos, finding keys (and protect them from non controlled aliens and countryes attacks and attacking citys) until countryes submit with u
4) Worst <--- U fail to do anything, your base is destroyed, countryes subit with hostle aliens.
Enemys:
Alien (mind controlled) <--- Blood needing aliens, need to save Mastercomputer from evil invaders(humans), They attack and explore randomly won't work together). Live everywhere on every (even small ships, think only on freeing computer and killing its enemys (you and friendly aliens)
Alien (free from control) <--- not under control, they try to free theyr mates from mind control. Live in a big mothership.
Humans <---- BAD ENDING u submit with mind controlled aliens and start killing countryes capitals and citys. Live on earth.
Computer self-defence units <--- Good and normal ending. They are cyborgs (robats that are strong) and remanats of old and weak alien empires (sectoids, floaters)
WHY?
??
-----Why won't aliens nuke earth----
Unfriendly aliens need to protect mother computer and friendly aliens try to save theyr mates.
---Why artifact hasen't been destroyed---
As it is very hard to destroy(it can be destroyed only from inside)
---Why it hasn't been found?---
Its hard to find and it can't be opened w.o. special keys that humans know as items of gods (thor hammer, zeus crown, devils horn ...)
---Who left/built it? Why? ---
Aliens, it had to be ultra secure info progressing machine that allowes brain to survive longer, also procress emutions and remove most hostility.
--- Why aliens attack citys---
Humans are threat to mind controlled aliens as humans might find a way how do destroy super comp. And they have incridible need for killing
--Why they kidnap us and explore our lands---
They(friendly aliens) try located keys and computer loaction and disabel it (not destroy it). But beacose humans and aliens attack them they must find a way to loacate keys fast. (human knows the keys)
---How to humans know about the keys---
Unfortunally humans don't know that until late in the game.They are objects of gods... how to humans know gods??? i have no idea.
--- Why we just can't give computer loaction to aliens (friendly or unfiendly?)
As aliens will continue terrorizing us and friendly aliens will tak e long time to recover keys cuz they don't know earth past or nothing about or gods.
(there still are many typos but i think its enough good...)
One thing i would like to add is: plz stop putting only US everywhere... i understand that most pp are from us, why can't phalanx be a Greater Eropian union or arfica spec unit.. Most likely is that phalanx is a org like WHO (world health organi.) And us can't be only country in world that has/had connections with aliens or some underground organizations ! why do u forget other countryes.......