Time for another "Book that Changed the World," yet another book I haven't read, but maybe you have. On War by Carl von Clausewitz, a nineteenth century Prussian war general, is considered to be one of the most important books ever written on war strategy, admired by everyone from Hitler to Colin Powell. War strategy's not really one of my leisure-reads, so thanks go to Hew Strachan for cutting to the chase with his book on the tome. Have you read On War? What's your vote for the most essential point of the book?