World Alliance mod for Half-Life 2

Late in the 30th century, a race of aliens that has been forced out of their home galaxy has found earth. Wandering the stars for centuries before coming upon our solar system, the aliens have had many years to perfect their technology. They have tried to claim many planets, but always have lost. So they retreat to the stars once again and search for a planet they can inhabit.

Finding earth the aliens decide that perhaps a different strategy is necassary, so they look upon our planet and study us for years, after watching and waiting for nearly a hundred years, they decide upon their plan. They will use their highly advanced technology to strike at our cities and homes, and then pull out before a sufficient resistance can amass itself. It is with this Hit and Run strategy that the aliens have wreaked havok upon our planet.

it is now the year 3000, the aliens have been attacking us for over a century, manking has fallen on its last leg. The leaders of the world have decided that no country can fight this menace alone, all countries and peaples are now united
in the World Alliance, and have massed an army capable of fighting back, trained to fight an enemy faster and stronger than them, these are the elite of mankinds armies.

And now the fight begins, the Fight for Earth.

But how little the humans knew about the aliens. Nothing short of the apocalypse would stop their deadly attacks, they had been driven from their homeworld and forced into the depths of space for Aeons before finding Earth. On their own
planet they were a peaceful race, in tune with nature, until a greedy race of space warriors came and slaughtered them by the thousands. The aliens raced to an ancient cave, a cave with walls of blood and doors of bone, a cave where the knowledge of how to kill was kept. They took the knowledge, and with it gained the knowledge of symbioses and where to find their ancient counterparts. They fought bravely, but ultimately failed.

Then they found humanity, they spent years studying this strange new creature, and decided to attack.

and the fight continues.