On 28 July 1914, Austria-Hungary declared war on Serbia. The rest of Europe would soon choose a side, and within a month the guns of August were sounding.
Although the world knew about the assassination of Archduke Franz Ferdinand in June, everyone expected the reaction to be localized and within appropriate bounds.
Everyone, that is, except anyone who had been privy to earlier discussions in the Austro-Hungarian court about how to get rid of Serbia. Or anyone who had been paying attention to the last few decades of back-and-forth proxy fighting between Austria-Hungary and Russia in the Balkans.
As Otto von Bismarck famously said in 1888, “One day the Great European War will come out of some damn foolish thing in the Balkans.“