On 28 June 1914, Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, was shot and killed in Sarajevo, Bosnia, by 19-year-old Gavrilo Princip, a Bosnian-Serb nationalist member of the secret society known as the Black Hand.
The assassination was almost accidental: an earlier attempt with a grenade that morning had failed, and Princip fired his shots only after stumbling upon the Archduke's car when it stopped, having taken a wrong turn. Austro-Hungary issued a deliberately harsh ultimatum to Serbia; when Serbia's response was deemed insufficient, Austria-Hungary declared war.
The system of European alliances — the Triple Entente (Britain, France, Russia) against the Triple Alliance (Germany, Austria-Hungary, Italy) — meant that within six weeks, all the great powers of Europe were at war. World War I claimed 20 million lives. A single assassination, in a city few Europeans could locate on a map, had ignited the most destructive conflict in history to that point.