Jingo by Terry Pratchett

World War breaks out on the Discworld in the twenty-first Discworld novel.
     Throughout history, there's always been a perfectly good reason to start a war. Never more so if it is over a 'strategic' piece of old rock in the middle of nowhere. It is after all every citizen's right to bear arms to defend what they consider to be their own. Even if it isn't. And in such pressing circumstances, you really shouldn't let small details like the absence of an army or indeed the money to finance one get in the way of a righteous fight with all the attendant benefits of out-and-out nationalism.