A major event that ignited World War I was the assassination of Archduke Franz Ferdinand of Austria on June 28, 1914. The Archduke was killed in Sarajevo by Gavrilo Princip, a member of the nationalist group known as the Black Hand, which sought to promote Serbian nationalism. This assassination set off a chain reaction of events, including Austria-Hungary’s declaration of war on Serbia, which triggered alliances and led to a broader conflict involving multiple nations. The intricate web of alliances, militarism, and nationalism in Europe contributed to the war's rapid escalation from this initial spark, ultimately resulting in a devastating four-year global conflict.