28 June 1914. The car turns the wrong way off Appel Quay and stalls as the driver tries to back up. Gavrilo Princip, nineteen, is standing outside a delicatessen with a pistol. Two shots. The Habsburg heir, Franz Ferdinand, and his wife Sophie are dead, killed by a Bosnian Serb cell on a Serbian national day.
Why then
The Balkans are leftover Ottoman ground being sorted by force. Serbia has come out of the Balkan Wars nearly doubled, and Austria-Hungary, an empire of a dozen peoples, fears what that does to its own Slavs.
What they wanted
Princip's people want South Slavs out from under Vienna. Austria-Hungary's foreign minister and army chief are after a short war that humbles Belgrade before the empire looks weak. Berlin writes a blank cheque, convinced its window against Russia is closing. Nobody is trying to start a world war. Several are trying to start a small one.
What changed
Within five weeks Russia, Germany, France and Britain are at war. Four empires, the Habsburg, Hohenzollern, Romanov and Ottoman, will not survive it. The Habsburgs wanted a lesson in the Balkans. They got a century.
Still argued
The shots are not in dispute. July is. Fritz Fischer argued that Germany used the crisis to bid for mastery of Europe; Christopher Clark spreads the blame across cabinets that walked into it half awake.