War among European nations erupted when?

War among European nations erupted when longstanding tensions, rivalries, and alliances culminated in the assassination of Archduke Franz Ferdinand of Austria-Hungary in June 1914. This event triggered a series of diplomatic failures and mobilizations, leading to the outbreak of World War I in August 1914. Nationalism, militarism, and imperial ambitions further fueled the conflict, drawing multiple countries into a devastating war that reshaped the continent.