‘How can one person lead one hundred?’ That was one of the questions in my Cambridge entrance exams back in 1981, and although I can’t now recall whether I tried to answer it in the three hours we were given, it has fascinated me ever since. So when I was given the splendid opportunity of delivering nine Lehrman Institute lectures on military history at the New-York Historical Society three years ago, I used them to try to answer it, at least in terms of war leadership.