What is it like to be in battle? John Keegan, a senior instructor at Sandhurst, the British Military Academy, speaks for soldiers who were present in the fray.

For examples, Keegan selects Agincourt in 1415, Waterloo in 1815, and the Somme in 1916. What is common about them, what is different? Agincourt was hand-to-hand combat, thrust and cut--a fearful and personal encounter. At Waterloo, 400 years later, the battle was still largely personal. As it swayed back and forth, men on opposite sides came to recognize the same individuals they had fought off in previous charges.

Keegan closes his book with the Somme. For him it stands as the distillation of wars in the industrial age: long-distance killing of faceless men by others who merely activate the instruments of destruction.

• historymilitary