Sci-Fi Book Group: The Forever War, by Joe Haldeman
Never mind the 100 years war. Private William Mandella is fighting a war that takes place over a period of 1000 years through the vastness of space and time. As Mandella suffers the effects of time travel to battle after battle throughout the millennium, he faces increasing doubts about the seemingly endless conflict with the Taurans, which surely echo the author’s own experience as a soldier in the Vietnam War.