On June 28, 1914, a young Serbian nationalist named Gavrilo Princip killed Archduke Franz Ferdinand, heir to the throne of the Austro-Hungarian Empire, in Sarajevo, Bosnia. Taking place against a backdrop of escalating tensions in the Balkans, the assassination set off a chain of events that would lead to the start of World War I barely one month later. To many people, the Great War—as it was known at the time—seemed to come out of the blue, as the European continent was enjoying a long stretch of unparalleled peace and prosperity. In fact, the seeds of the devastating conflict had been planted long before Princip fired those fatal bullets