When Franz Ferdinand and Sophie Chotek arrived at Sarajevo train station on the morning of 28 June 1914, Europe was still at peace. If any of the key European statesmen of that era had been asked whether they thought a major European conflagration was likely in the near future, they would all have replied that a major war had, in fact, been getting less likely in the past two years. The reason, above all, was because the two recent Balkan wars had come and gone without triggering a wider European conflict. Crises seemed to crop up without descending into a full-blown continental war between the great European powers.

In her latest book, Margaret Macmillan makes the point that the drumbeat of repeated crises, before 1914, rather than reminding Europeans to remain alert to the dangers of a major war, had in fact the opposite effect, it numbed or deadened their…