Ibid., pp. 97–118; John Keegan, A History of Warfare (London, 1993), pp. 202–08; Robert L. O’Connell, Ride of the Second Horseman: The Birth and Death of War (New York and Oxford, 1989), pp. 171–73; R. D. Sawyer, The Military Classics of Ancient China (Boulder, Colo., 1993)