It was sort of out of his hands. Things were already set in motion with alliances. He was thoroughly shackled to the interests and actions of Austro-Hungary, and it soon became apparent, as the war pressed on, that he was "shackled to a corpse."
Also we have the nature and character of the kaiser. He had had dinner with the Archduke and his wife a week before they were shot to death. He was impressed, infuriated at the nerve of the "peasants" who dared raise their hand against their "masters", and also was disappointed that the new archduke didn't rush things to supress the rebelion in the Balcans. So, even conceding that he might have not had other choice but to go to war with Austria, he wasn't really doing much to stop the events.