 The Second World War, of course, was the most devastating war arguably in the history of the world. Close behind it is the First World War. And what is the lesson of the First World War? It's not that there are always people appeasing the bad guys or fighting against the bad guys. The lesson of World War I is that if you're not careful, you can blunder yourself into a broader regional conflict that kills tens of millions of people, many of them innocent.