This tag should be used for questions related to the 1974 novel "The Forever War" by Joe Haldeman.
The Forever War is a well-known science fiction novel written by American author Joe Haldeman, originally published in 1974.
The story is notable for its depiction of interstellar war in the context of a technology suite that does not allow for non-Einsteinian travel: Although starships reach relativistic velocities, they also undergo time dilation. This causes multiple problems in communication and logistics, and it ensures that any soldier who embarks on a mission will be functionally "dead" from the standpoint of anyone left behind, as decades or centuries will have passed locally before the soldier can return.
The book is generally considered to present an anti-war theme, and it contains many elements that can be allegorically mapped to the experiences of United States soldiers during and after the Vietnam War. Haldeman himself was a veteran of that war.