Jicksy was a little alien that would bite into humans in their sleep. They would then go through an involuntary transformation.
Then being repulsed by the Earth’s atmosphere and food, these new “metamorphosed green humans” eagerly sought refuge on the moon. These humans and the aliens had a deep love for one another too.
Once established, other humans willingly followed suit and Jicksy went into hot demand for her “transformation service.”
Earth was in a state of war anyway. It was a dangerous place to be. Much of this war was orchestrated by the aliens behind the scenes. These aliens had both envy and awe for the humans, and a fetish for Earth’s iconic structures.
For the aliens, it was also a way to signal dominance to other alien races who had being seeking inroads into Earth for a very long time without much success. So it gained them much needed allies.. and enemies.