XCOM 2 War of the Breeder

Aliens had invaded earth, and the old XCOM forces managed to push them back to the point they declared peace, they offered the governments technology and aid in return for cooperation and becoming part of the collectives forces. Little did Humanity know that the aliens needed humans, or more precisely human females to breed with. Their gene therapy clinics were there not to just help humanity, but to also augment them to be more fertile and be more compliant to their new overlords.

XCOM saw the writing on the walls and quickly managed to steal an alien ship, the avenger. After outfitting the ship and gathering what remains of the old XCOM operatives they fought the aliens for months before realizing a major issue, the aliens had pheromones they developed that made men turn to a form of lost that wanted nothing but sex, in turn all combatants going forward had to be female. This in turn caused the aliens to aim to capture instead of kill when they faught XCOM forces.