The aliens are a race of beings who travel around, making planets livable by first making them able to be lived on by human beings, and then by placing human beings on the planet, so that the humans will then further develop the planet, as well as providing meat for the aliens when they return to live on the planet that they cultivated.
They developed a technology called 'summoning' which involves a large 'altar' inside a pentagram of 'control points (we should figure out a name for them).' The aliens would 'sacrifice' an alien or a different animal on the altar, at the same time as all of the control points were activated, which would then turn the sacrificed being into a larger version of itself, believed to be invincible (until the human one kicked its ass).
The second, warrior race of aliens, now summons larger demons, which are basically the same size as human demons.
The aliens are masters of organic material, meaning that their weapons are centered around organic material.
The alien race began cultivating earth by making the planet livable, then creating humankind and other animals to live on the planet.
They soon realised that this 'batch' of humans was becoming too violent, and that they might attack the alien race, so they built altars around Europe, and began creating 'demons.' Unfortunately, the humans began mimicking aliens, and because the aliens were only at that point a weak harvesting species, the sacrifices on the altar were only weak compared to the humans' sacrifices, who turned into gargantuan titans, beating the aliens easily.
The aliens were forced to retreat, and left the planet to run itself, but they created a prophecy in their species which would eventually threaten to destroy humanity.
The prophecy told of a time in the far future, when the humans who were now mere cavemen, would evolve and become intellegent. They would invent tools, weapons, and eventually, spacecraft. Then, humankind would come looking for the aliens who created them, and overpower them.
Because of this prophecy, the aliens created a seperate division of their race, who would grow in strength and number, so that when the bad batch of humans finally found their way into space, they wouldn't be a threat.
The new race was trained in summoning demons, now much stronger and larger, as well as in combat.
In the year 2105, humanity found its way into deep space, out of the galaxy that the aliens had avoided for so long, and into the greater solar system. This was met by the aliens with large numbers of spacecraft, which forced the small amounts of human spacecraft back to earth.
A single alien spacecraft landed on earth, in Australia. The troops from that spacecraft found the altar in Australia, and summoned a demon. Unfortunately, this demon was defeated, and the altar was controlled by the humans.
The humans learnt about the altars. They found all of the altars in Europe, and now they want to control them. The aliens are sending spacecrafts to each altar in Europe, in an attempt to obtain control of these altars.