I read this to take part in the twitter #sfbookclub. I'm pretty surprised that I never got around to reading it earlier. Due to time dilation, our hero (a pacifist scientist) manages to participate in major conflicts across the span of a 1000 year interstellar war. Earth and humanity change out from under him in during each deployment. The novel loosely explores some science fictional themes but mainly establishes a strong allegory for the very real dissociation that all military people experience after combat.

I'd place this on ANY list of must read science fiction books as well as any must read books of military fiction.