Two SF books about War.
“The Forever War” by Joe Haldeman
“Starship Troopers” by Robert A. Heinlein
Joe Haldeman wrote “The Forever War” about his experience in Vietnam, an SF book about a war which goes on for hundreds of years, and due to relativity (thanks, Einstein!) moves into the future only to find out the war is just a mistake. Originally published in the late 70s, the book is still relevant.
If you had only seen the movie version of “Starship Troopers”, the book will be a real surprise. The main characters are black Brazilians defending Earth against aliens, or maybe not.
It provides a great contrast to “The Forever War” and certain current events.