There were several main causes of World War I, which broke out unexpectedly in June–August 1914, including the conflicts and hostility of the previous four decades. Militarism, alliances, imperialism, and ethnic nationalism played major roles. However the immediate origins of the war lay in the decisions taken by statesmen and generals during the July Crisis of 1914, which was sparked by the assassination of Archduke Franz Ferdinand, heir to the throne of Austria-Hungary, by a Serbian secret organization, the Black Hand.