How did a wrong turn in Sarajevo help start World War I?

It put the heir to the Austro-Hungarian throne in front of a gunman who had already given up. On 28 June 1914, six young conspirators lined the route of Archduke Franz Ferdinand's motorcade in Sarajevo. One threw a bomb, which bounced off the archduke's car and exploded under the next one. The others failed to act as the cars sped past. The plot seemed to have failed.

After a reception at the Town Hall, General Oskar Potiorek decided the cars should drive straight along the riverside to the hospital, avoiding the city centre. But nobody told the drivers. At the Latin Bridge, the archduke's driver, Leopold Lojka, followed the cars ahead into a side street. Potiorek shouted that he was going the wrong way. The driver braked, tried to reverse, and stalled the engine, right next to where the teenage Gavrilo Princip was standing. Princip stepped onto the footboard and shot Franz Ferdinand and his wife Sophie at point-blank range. (The popular tale that he had just bought a sandwich has no source from the time.)

The wrong turn did not cause the war on its own. Europe was already divided by rival alliances and an arms race. But the killing set off the July Crisis: Austria-Hungary sent Serbia an ultimatum designed to be rejected and declared war on 28 July, Russia mobilised, and within a week Germany, France and Britain were at war. Some 15 to 22 million people would die.