Military science fiction stories happen during wars. These wars can be between different countries, different planets, or between different species. The stories are told by characters who are soldiers. They include detail about military technology, rules, and history. Some Military SF may be similar to real historical conflicts. Heinlein's "Starship Troopers" is an early example. Another is the Dorsai novels of Gordon Dickson. Joe Haldeman's "The Forever War" is a response to the World War II–style stories of earlier military SF authors. Haldeman was a soldier in the Vietnam War. Important military SF authors include John Ringo, David Drake, David Weber, and S. M. Stirling. Baen Books is known for cultivating military science fiction authors.