ORIGINAL: altipueri
Strikes me as showing Austria-Hungary caused it then. They cashed the blank cheque.
The Austrians obviously wanted war with Serbia, because Serbia was indeed a very destabilizing power in the Balkans. Conrad von Hotzendorf was badgering Kaiser Franz Joseph to declare war on Serbia basically every day they were formally meeting, and for good reasons. Serbia, with its very existence, stirred nationalist dissenters among the differents nationalities in the Empire with this dream of a unified Serbian Empire, which included territories held by Austria, like Bosnia. Plus, their government was run by a number of thugs and regicides, which did not improve matters.
It is not war with Serbia that caused the First World War. It is in part the clumsy manner which Austria-Hungary went to it due to various factors like needing conscripts for harvest, the veto from Count Tisza and Hungary's cabinet, the sheer slowness of Habsburg government protocols, etc. Their mute silence for weeks after Franz Ferdinard's assassination, immediately followed by a sudden, rash, and totally unacceptable ultimatum at the end of July was astonishing to all European governments. Vienna's slowness in acting allowed time for Russia to mobilize, their obvious bad faith sickened all the other powers' chancelleries, and Serbia's genial reply succeeded in mustering international sympathy as the victim of Austrian bullying.
While Kaiser Wilhelm had a
lot of flaws, he was an intelligent man and sometimes, despite his impulsiveness and his mercurial, insufferable temper, he assessed things right. Had the Austrian army listened to him and Bethman-Hollweg and did as they recommended, chances are it would have ended with a peace conference, not four years of all-out war. Vienna interpreted this "blank cheque" as doing as they pleased. Kaiser Wilhelm gives this "blank cheque" on the condition that Austria acts immediately and occupies Belgrade as a bargaining chip.