The Forever War by Joe Halderman
This one has been on my todo list for some time.
The Forever War (1974) is a military science fiction novel by American author Joe Haldeman, telling the contemplative story of soldiers fighting an interstellar war between Man and the Taurans. The futile, meaningless war, which had lasted for more than a thousand years.
Perceived to be a portrayal of the author’s military service during the Vietnam War, and has been called an account of his war experiences written through a space opera filter. The alienation experienced by the soldiers on returning to Earth becomes a clear metaphor for the reception given to US troops returning to America from Vietnam, including the way in which the war ultimately proves useless and its result meaningless. Still reading through but hope to finish shortly.