The Western Front of the Great War is one entirely of Germany's making. Germany attacked Belgium and France first and it was moreover Germany which pushed Austria-Hungary to present impossible demands to Serbia while telling them Russia would do nothing. The person and indeed the organization which killed Franz Ferdinand - Young Bosnia, wasn't Serbian in origin and its connections to the Serbian Black Hand was dubious and its not like the Austrians ever performed an actual investigation into it. Nonetheless, the Serbian Government tried and executed the entire organization in 1917 because the Serbian Government was just as annoyed by the Black Hand as the Austrians were.