I'm trying to find a book I read ages ago; it was a space opera style sci-fi story about aliens contacting humans and then bringing them into a war against a hostile alien species. In this story however, humans were tougher than just about every alien species and crucially they had innate mental resistance to the hostile alien species mind control.
It's been a long while since I read it but; In the story the humans are considered special because Earth has a moon which means the humans are more powerful due to (effect I forget) at the very end of the battles (it may be a series, it's been easily 10 years or more since I read it) the hostile aliens surrender to the allied forces (including the humans) which throws everything up into the air. At that point the human sides start slowly breaking out into war against themselves on the other planets they've been allowed to settle on. Also part way in the stories (I think it was a series?) the hostile aliens have created a camp on a planet they control where humans are raised thinking they are actually aliens, not humans, in an effort to understand and control humans.