"World War I still haunts us, partly because of the sheer scale of the carnage—10 million combatants killed and many more wounded. Countless civilians lost their lives, too, whether through military action, starvation, or disease. Whole empires were destroyed and societies brutalized.

But there’s another reason the war continues to haunt us: we still cannot agree why it happened. Was it caused by the overweening ambitions of some of the men in power at the time? Kaiser Wilhelm II and his ministers, for example, wanted a greater Germany with a global reach, so they challenged the naval supremacy of Great Britain. Or does the explanation lie in competing ideologies? National rivalries? Or in the sheer and seemingly unstoppable momentum of militarism? As an arms race accelerated, generals and admirals made plans that became ever more aggressive as well as rigid. Did that make an explosion inevitable?

Or would it never have happened had a random event in an Austro-Hungarian backwater not lit the fuse? In the second year of the conflagration that engulfed most of Europe a bitter joke made the rounds: “Have you seen today’s headline? ‘Archduke Found Alive: War a Mistake.’” That is the most dispiriting explanation of all—that the war was simply a blunder that could have been avoided.

The search for explanations began almost as soon as the guns opened fire in the summer of 1914 and has never stopped. Scholars have combed through archives from Belgrade to Berlin looking for the causes. An estimated 32,000 articles, treatises, and books on World War I have been published in English alone. So when a British publisher took me out to lunch on a lovely spring day in Oxford five years ago and asked me if I would like to try my hand at one of history’s greatest puzzles, my first reaction was a firm no. Yet afterward I could not stop thinking about this question that has haunted so many. In the end I succumbed. The result is yet another book, my own effort to understand what happened a century ago and why."

A set of 8 podcasts being aired between 28 June and 4 August 2014. Recorded with the UK Foreign Secretary and former British Ambassadors to the key European countries involved in the First World War (Austria, Belgium, France, Germany, Russia, and Serbia).

Why did a small number of European statesmen take the world into the seminal catastrophe of the Great War? The German Chancellor Otto Bismarck had warned in 1880 that “some damned foolish thing in the Balkans” might lead to a terrible war. The shots at Sarajevo did just that a hundred years ago. What have we learned?