When it came to assigning guilt for the cataclysm that led to the horrors of the twentieth century in Europe, all five major players in the events that launched World War I—Germany, France, Austria-Hungary, Russia, and Great Britain—claimed innocence. The record of intricate and complex diplomacy and alliances among these powers in the run-up to the Great War often ignores the role of Serbian nationalism and the signal moment it produced: the assassination of the Austrian archduke Franz Ferdinand and his wife Sophie in Sarajevo on the morning of Sunday, 28 June 1914, by Serbian terrorists. It put an exclamation point on the political tension and instability of the Balkans in the years before the outbreak of war. In his new book The Sleepwalkers (called by the New York Times “a masterpiece”), Christopher Clark tells how the European continent, seemingly at peace, fell into war just thirty-seven days after the incident at Sarajevo. The assassination of the archduke, Clark argues, was not a marginal act, as many historians have suggested, but a key provocation. The conflict that began that summer mobilized 65 million troops, claimed three empires, 20 million military and civilian deaths, and 21 million wounded. The American historian Fritz Stern called it “the first calamity of the twentieth century, the calamity from which all other calamities sprang.” The Old World aspects of these events disguise some very modern elements in the assassination at Sarajevo: a cavalcade of automobiles, a squad of suicide bombers, and “an avowedly terrorist organization with a cult of sacrifice, death, and revenge” that existed across political borders, without a clear location. Here in gripping detail is the story of what happened on that fateful morning in Sarajevo.