'If you want peace, prepare for war," counseled the Roman general Flavius Vegetius Renatus more than 1,600 years ago, echoing the sage advice given nine centuries earlier by the Chinese military strategist Sun Tzu. But in a film I saw recently at Oslo's Nobel Peace Center, this ancient wisdom was turned on its head: "If you want peace," it said, "prepare for peace." This purports to be wise counsel, a motto for the millennium. In reality, it's wishful thinking that doesn't follow logically from the history of war, the real lesson of which is the one that Sun Tzu and...