Answer: The assassination of Archduke Franz Ferdinand and his wife, Sophie
Explanation: The direct event that started the First World War is the assassination of Archduke Franz Ferdinand and his wife, Sophie. Although there were many other imperialist reasons, as well as the aspiration of ethnic groups for freedom, this event marked the direct reason for referring ultimatum to Serbia by Austria-Hungary, the Serbian refusal of the ultimatum and declaration of war on Serbia on July 28, 1914. Subsequently, Russia and the Germans they entered the war and then many other great powers.