The main cause of World War I, also known as the Great War, was a complex combination of political, economic, and military factors. However, the immediate trigger for the war was the assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, in Sarajevo, Bosnia, by a Serbian nationalist. This event set off a chain reaction of diplomatic crises and military mobilizations among the major European powers, leading to the outbreak of war. The assassination of Archduke Franz Ferdinand became the catalyst that ignited the pre-existing tensions and rivalries among the major powers, leading to a widespread conflict that eventually engulfed much of the world and resulted in the loss of millions of lives.