Europe was at peace on the morning of Sunday 28 June 1914 when Archduke Franz Ferdinand arrived in Sarajevo. Thirty-seven days later it was at war. As the American historian, Fritz Stern put it, this war was “the first calamity of the 20th century, the calamity from which all other calamities sprang.” So begins ‘The Sleepwalkers’ Christopher Clark’s masterpiece on the origins of the First World War. The absence of war from Europe for nearly three decades risks sleepwalking the continent into the most significant conflict in a generation. Diplomacy may yet succeed. However, Russia’s belligerence towards Ukraine has put…