Exactly one month after Gavrilo Princip's bullets killed Archduke Franz Ferdinand in Sarajevo, Austria-Hungary declared war on Serbia. The declaration triggered mobilization clauses across Europe's alliance system, drawing in Russia, Germany, France, and Britain within days. What began as a Balkan punitive expedition became a four-year conflagration that killed some 17 million people and toppled four empires.
The declaration itself was almost anticlimactic, a formal telegram sent by Austro-Hungarian Foreign Minister Leopold Berchtold to the Serbian government after Belgrade failed to satisfy an intentionally harsh ultimatum. Vienna wanted a short, punitive war to crush Serbian nationalism once and for all. Kaiser Wilhelm II had already given Austria-Hungary a so-called 'blank check' of support weeks earlier, believing Russia would not intervene.
He was wrong. Russia, bound by treaty and pan-Slavic sentiment, began mobilizing in support of Serbia within days, and the interlocking system of alliances that European statesmen had built over decades to preserve peace instead guaranteed catastrophe. Germany declared war on Russia on August 1 and on France two days later, then invaded Belgium to reach Paris quickly, pulling Britain into the war on August 4.
Few who cheered the declaration in Vienna's streets imagined trench warfare, poison gas, or the collapse of the Habsburg, Romanov, Ottoman, and German empires. The war Austria-Hungary launched to survive as a great power instead destroyed it entirely, along with the old European order it was meant to preserve.