The assassination of Archduke Franz Ferdinand of Austria on June 28, 1914, was the pivotal event that triggered World War I. His murder in Sarajevo by a Bosnian Serb nationalist set off a chain reaction of alliances and tensions that had been building in Europe. Austria-Hungary's subsequent declaration of war on Serbia activated a series of alliances involving major powers like Russia, Germany, and France. The conflict escalated into a global war that lasted until 1918, reshaping international relations and leading to significant socio-political changes in many countries, including the formation of new nations and the rise of communism in Russia.