The forever war
(Book)

"He went off to war, but the Earth he came back to wasn't the one he left behind Man has taken to the stars. Deep in space, humans discover the fearsome Taurans after a transport ship is destroyed. To combat the threat, humanity sends in the United Nations Exploratory Force-a highly trained unit built for revenge. Conscripted into the service, physics student William Mandella fights for his planet against the alien force light years away. However, because of the relative passage of time when one travels at incredibly high speed, the Earth he returns to after his two-year experience has progressed decades and is foreign to him in disturbing ways. Based in part on the author's experiences in Vietnam, The Forever War is regarded as one of the greatest military science fiction novels ever written, perfectly capturing the alienation that servicemen and women experience even now upon returning home from battle" --Publisher.