The assassination actually gives Austria the excuse it’s wanted to crush Serbian nationalism. Soon after the assassination, Austria secures Germany’s support to guard against Russian involvement, as they issue a demanding ultimatum to Serbia that isn’t fully met. This results in the bombing of Belgrade and a declaration of war against Serbia on July 28, 1914. This, of course, sparks WWI as a result of all the entangled alliances among the combatants, with each side declaring war on the other.