John Keegan

Soldiers, when committed to a task, can't compromise. It's unrelenting devotion to the standards of duty and courage, absolute loyalty to others, not letting the task go until it's been done.

Of whatever class or nation, however, all successful participants in the repetitive and unrelenting stress of aerial fighting came eventually to display its characteristic physiognomy: skeletal hands, sharpened noses, tight-drawn cheek bones, the bared teeth of a rictus smile and the fixed, narrowed gaze of men in a state of controlled fear.

Men killing other men really is an extraordinary phenomenon. Why does it happen? And how long has it gone on? And have the motives changed?

The Second World War is the largest single event in human history, fought across six of the world's seven continents and all it oceans. It killed 50 million human beings, left hundreds of millions of others wounded in mind or body and materially devastated much of the heartland of civilization.