The First World War has cast a long shadow over the twentieth century, and beyond. One hundred years on, the horror of the conflict still commands attention, and will probably never cease to do so. How and why the civilized world, seemingly so secure in its material and intellectual achievements, could have descended into a global conflict has continued to intrigue not just historians, but also the general public. It has certainly puzzled me ever since I first developed an interest in the past. And the more I studied the period of the long nineteenth century, the more it became clear to me that the answer, in so far as there can be one, is not to be found in les forces profondes, the vast impersonal forces, that some think shape historical processes, but, rather, that the reasons, in so far as they can ever be fathomed, may be glimpsed in the doings of men (and they were all men in 1914), their flaws and failings, their calculations and miscalculations. It would be difficult to improve on Marx’s insight that people make their own history, if not under circumstances of their choosing. Politics more especially are subject to the ambiguities of free will and the play of the contingent. In that lies hope for the future; but it is also a reminder of man’s shortcomings. What follows here is an attempt to make sense of the events of Europe’s last summer.