The Start of World War I refers to the beginning of one of the deadliest conflicts in history, ignited by the assassination of Archduke Franz Ferdinand of Austria on June 28, 1914. This event set off a chain reaction of political alliances and militaristic posturing among European powers, leading to the widespread mobilization of troops and the declaration of war in August 1914. The conflict resulted from a mix of nationalism, imperial ambitions, and intricate alliance systems that had developed in the years preceding the war.