The heritage trilogy, book 3 : Europa strike
Ian Douglas2000

The final conflict

Chaos has erupted throughout the known galaxy, threatening countless colonies and orbital habitats - as the Associative struggles vainly to keep the peace. Extreme measures are called for in these times of dire crisis, and the Star Marines are awakened from their voluntary 850-year cybe-hibe sleep. But General Trevor Garroway and his warriors are about to discover that the old rules of engagement have drastically changed . . .

The end begins with an old-style assault on rebels at the Tarantula Stargate. But true terror looms at the edges of known reality. Humankind's eternal enemy - the brutal, unstoppable Xul - approaches, wielding a weapon monstrous beyond imagining. Suddenly not only is the future in jeopardy, but the past is as well - and if the Marines fail to eliminate their relentless xenophobic foe once and for all, the Great Annihilator will obliterate every last trace of human existence.