"It was not worth even one life," said Harry Patch shortly before he died in 2009 at the age of 111. He was the last survivor of the 65 million soldiers who fought in World War I — which for Britain began 100 years ago this week — and by the time he died it was a normal, quite unremarkable thing to say. But he would never have said it in 1914.

Very few people thought that war was a bad thing in 1914. Losing a war could be a bad thing, but the obvious solution to that problem was to be very good at war. Human beings had always fought wars, military values were deeply embedded in our culture, and nobody expected those attitudes to change. And then they did change.

World War I was a human tragedy, of course, but this was when the human race began to question the whole institution of war: how useful it is, but also how inevitable it really is. And the answer to both questions is: not very.