Aliens: Colonial Marines sucks bad. I mean, even the modern day military has better tactics when dealing with beings like Xenomorphs assuming modern day weapons works against them in Alien vs Predator, then the modern day army might stand a chance.
So here's the deal. A Predator space craft falls in the ocean, but a mature Queen survive and swims to Africa. She arrives in Somalia and quickly starts creating it's facehuggers and hives. She impregnates a good number of people in a village and erases many para-military and bandits from the region who attempt's to enter in a cavern said to be dwell by "Black Demons Made of Gold". The xenomorphs has a month to prepare until the military realize how screwed they are.
The xenomorphs can use every life form and advantage they can get and as well as the military.