An immensely effective audit of how and why the Old World's aristocratic leaders failed to keep the peace during the summer of 1914. Jannen, a lawyer and historian, provides a riveting day-by-day account of the diplomatic and military machinations that began on June 28 when the heir to the Austro-Hungarian Empire's throne was assassinated in Sarajevo and ended early in August with all of Europe (save Italy) embroiled in WW I. The author first reviews events leading up to that critical period: the commercial rivalries, recurrent crises, and largely defensive alliances that by 1914 had divided the Continent into volatile armed camps. Getting down to cases, he notes that Vienna's determination to punish upstart Serbia for the murder of Archduke Francis Ferdinand (and to halt the spread of Balkan nationalism) was the proximate casus belli. Despite the best efforts of Europe's rulers, however, it was impossible to localize the conflict. Offering vivid reports on the frantic negotiations that preceded Austria's declaration of war, Jannen recounts how Russia (at least tacitly committed to hacking fellow Slavs in Belgrade) mobilized its armed forces along the Austrian and German frontiers. Bound by treaty and inclination to support Vienna, Berlin declared war on Russia; two days later, France was added to the list of German foes. Great Britain was drawn in by an 1839 accord with Brussels when the kaiser's troops marched through Belgium on their way to France. By the time the guns of August fell silent more than four years later, millions had died while three dynasties vanished, the map of Europe was rearranged, and precious few spoils went to the victors. An object lesson in history that affords resonant behind-the-scenes perspectives on the games great and small powers play in time of peril. An absorbing and scrupulously documented first book.