The event that triggered the start of World War I in 1914 was the assassination of Archduke Franz Ferdinand of Austria on June 28. This assassination, carried out by Gavrilo Princip, a member of a nationalist group, set off a chain reaction of alliances and mobilizations among European powers. Austria-Hungary issued an ultimatum to Serbia, which ultimately led to the declaration of war. The complex web of alliances—between the Allied Powers and Central Powers—intensified the conflict, leading to a full-scale war that lasted until 1918 and had profound consequences for global politics and society.