Allow me to fill you all in. The Alien universe is more of a book story, the movies just help those of us who hate reading (I'm one of them). Thankfully a buddy of mine reads the books like a religious affair and fills me in on the stories.
Aliens, Preditors, and Humans are all part of the universe and in the future we all discover eachother in one way or another (won't get into it). Preditors are born hunters and hunted the Aliens for years but got bored as to how easy it was to kill them. To the Preditorean race Aliens are simple, stupid, and boring creatures to hunt. Then they see the little humans and go, "Oh yay a race of living organisms that actually have cognitive thinging, reasoning, and intelligence!". So the Preditors hunt humans because they are more difficult to kill and pose a larger danger. In this whole story of centuries of fighting a few crazy things happened, such as: Aliens took over Earth, we left. Much later we blew Earth to hell, and took it back.
I'm not sure what the story is in this new movie, nor does my friend, but the whole "Aliens vs. Preditor" idea has been around for a long time in books. Alien 1,2,3 were good. Alien 4 was a total piece of crap and made up by some moron. When Riply died, she died! None of this, "Oh lets clone her.", moronic crap ever happened.
K, I'm done.