Many years ago, I went to the Central Lobby of the Houses of Parliament in London to keep an appointment with the almost picturesquely reactionary Conservative politician Alan Clark. He was the son of Kenneth (later Lord) Clark—the art historian and author of the Civilisation series—and the heir to Saltwood Castle, in Kent. He was also the author of a 1961 book, The Donkeys, which was a history of the British General Staff in the First World War. The title came from a famous comment that had supposedly been made at that epoch by a German military strategist. Told by...