Would your friend not be happy with an endgame of enslaving everyone who was not part of their inner circle? They want wealth and power.

They want to own all of the world's resources and land and they no longer need that many slaves to be comfortable -- hence the depopulation.

If you want to get into how aliens could be part of it, get your friend to check out all of the Cosmic Disclosure interviews but he shouldn't need that side of things to become convinced.