The Forever War by Joe HaldemanRead about another entry on the list.
Another example of building on a theme. Haldeman’s first book, War Year, is a Vietnam tale, drawing on Haldeman’s experiences in that war. With his followup, he took those same experiences and set them in space.
Removed from the real-world political baggage of a very recent, very painful conflict, Haldeman’s second book used sci-fi as a metaphor. A quirk of light-speed travel means that, despite feeling like they’ve been away for a matter of months, centuries have passed for a group of returning soldiers. The world has changed, just as the world seemed very different to returning Vietnam veterans. By setting a familiar conflict in an unfamiliar setting, Haldeman made his readers experience the horrors of conflict afresh.
The Forever War made Sean Danker's list of five favorite SF books about war and military culture, Becky Ferreira's top ten list of best books for fans of The Twilight Zone, Emily Stamm and Charlie Jane Anders's list of the ten best science fiction stories where humans are the villains and Charlie Jane Anders's list of the 12 greatest science fiction war stories.