Caustic by Timothy A.
Synopsis: Earth has made first contact, but when our alien counterparts decide they want to set a couple thousand dyson spheres around our sun and kick us to the curb that first contact means war. Through genetic re-engineering, mutation, and cybernetic implants the human race rushes to evolve and fight on equal footing against the alien threat. Unfortunately for Earth it only took the alien armada a week to destroy the world. Caustic is the sad story about first contact with a superior species, war, and the years of survival that follow.