The immediate cause of the 1914 assassination that led to World War I was the killing of Archduke Franz Ferdinand of Austria and his wife, Sophie, on June 28, 1914, in Sarajevo, Bosnia. The assassination was carried out by Gavrilo Princip, a member of the nationalist group known as the Black Hand, who sought to promote Slavic nationalism and independence. This event set off a chain reaction of political alliances and mobilizations among European powers. The assassination ultimately triggered a complex web of alliances, leading Austria-Hungary to declare war on Serbia, which escalated into a full-scale global conflict known as World War I.