Austria had a deep seated hated for the Serbs partially due to their problems in the Balkans, and the assassination of Franz Ferdinand sealed the fate of WWI. William II initially gave Austria assurances of German support in the event of war and essentially told Austria to crush the Serbian problem before it got out of hand. When Austria declared war on Serbia after the assassination, it guaranteed both Russia (as Serbia’s protectorate) and Germany (as Austria’s ally) would join the war. Russia began to mobilize, which required Germany to move fast in order to execute the Schliefffen plan.