Extremis - Charles E Gannon

Once before, the sentient races in the known part of the galaxy - humans, Orions, Ophiuchi, and Gorm - had united to defeat alien invaders. Decades later, the member planets of the alliance had grown complacent - until a huge fleet of ships, each ship larger than a city, arrived, fleeing the loss of their home planet when their star went nova. They have traveled for centuries, and now that they have arrived at the world they intend to make their new home, they have one thought on their mind - conquest! They will exterminate all humans and their allies... unless the old alliance of humans and other beings can stop them!