Karl von Clausewitz´s study On War was described by the American strategic thinker Bernard Brodie as ´not simply the greatest, but the only great book about war´. It is hard to disagree. Even though he wrote his only major work at a time when the range of firearms was fifty yards, much of what he had to say remains relevant today. Michael Howard explains Clausewitz´s ideas in terms both of his experiences as a professional soldier in the Napoleonic Wars, and of the intellectual background of his time.