The Return - David Nash - Bog

After destroying the supercomputer overloads that were enslaving humans and turning them into mind-controlled zombies, A worse enemy appeared. While seeking out allies in their battle of man versus machine they caused the Ancient enemy of the computer race to return to the Orion arm of the Galaxy and claim Earth.
After learning of the Alien ability to destroy planets and teleport warriors on command, the elected leadership forsakes the Legion and orders them to disband.
Earth now serves a race of advanced gorilla warriors. Of course General Davis mutinies and leads a fraction of the Legion as the battle an enemy with the power to turn entire planets into battle ships.