“Honorable Opponent,” Clifford Simak, 1956 — A general can’t understand why his alien opponents don’t conform to the traditional practices of war until he realizes that they consider war a game. They have no need to negotiate the surrender or the return of captured ships; they’ll return them at conclusion of game.
Comments: Read in the Third Galaxy Reader.
Author: Wikipedia: “Clifford Donald Simak (August 3, 1904 – April 25, 1988) was an American science fiction writer. He was honored by fans with three Hugo awards and by colleagues with one Nebula award and was named the third Grand Master by the Science Fiction and Fantasy Writers of America (SFWA) in 1977.”