When a Serbian-backed assassin gunned down Archduke Franz Ferdinand in late June 1914, the world seemed unmoved. Even Ferdinand’s own uncle, Franz Josef I, was notably ambivalent about the death of the Hapsburg heir, saying simply, “It is God’s will.” Certainly, there was nothing to suggest that the episode would lead to conflict—much less a world war of such massive and horrific proportions that it would fundamentally reshape the course of human events.

As acclaimed historian Sean McMeekin reveals in July 1914, World War I might have been avoided entirely had it not been for a small group of statesmen who, in the month after the assassination, plotted to use Ferdinand’s murder as the trigger for a long-awaited showdown in Europe. The primary culprits, moreover, have long escaped blame. While most accounts of the war’s outbreak place the bulk of responsibility on German and Austro-Hungarian militarism, McMeekin draws on...