The Once and Future King Book 2, Chapter 4
Arthur, Kay and Merlyn continue to discuss whether a war could ever be a good thing. Merlyn says it could not, because no matter how terrible someone is, they can always be stopped by reason rather than war, and therefore, whoever makes the first move toward real warfare is always the one most in the wrong. Merlyn tells Arthur: "Unless you can make the world wag better than it does at present, King, your reign will be an endless series of petty battles..." Book 2, Chapter 4, pg. 241