Archduke Franz Ferdinand was heir to the Austro-Hungarian throne - one of the most powerful empires in Europe. He was visiting Sarajevo on June 28, a date of Serbian nationalist significance (the anniversary of the 1389 Battle of Kosovo). His presence was a provocation.

The archduke was not popular. His marriage to Sophie Chotek, a Czech countess, had been deemed beneath his station - their children were excluded from succession. But he was next in line for the throne, and his death would have consequences. The nationalists who planned his assassination hoped to spark a Serbian uprising. They got something much larger.

The assassination was planned by the Black Hand, a Serbian nationalist organization, and carried out by six young Bosnians armed with bombs and pistols supplied by Serbian military intelligence. They positioned themselves along the archduke's motorcade route through Sarajevo.

The plan was simple: as the motorcade passed, one of them would throw a bomb or fire a shot. If the first failed, the second would try. Then the third. Six chances to kill the archduke. What could go wrong?

Everything went wrong. The first two assassins in line lost their nerve and let the motorcade pass. The third, Nedeljko Čabrinović, threw his bomb - but it bounced off the folded-back convertible top and exploded under the following car, injuring bystanders. Čabrinović swallowed a cyanide pill and jumped into the river. The cyanide didn't work. The river was four inches deep.

The motorcade sped away. The remaining assassins, including Gavrilo Princip, dispersed. The plot had failed. Franz Ferdinand continued to city hall, where he complained about the bomb attack, then decided to visit the wounded in the hospital.

The driver of the archduke's car, unfamiliar with Sarajevo, was not informed of the changed route to the hospital. He turned onto Franz Josef Street - the original route - and drove directly past Moritz Schiller's delicatessen, where Gavrilo Princip had stopped, perhaps to buy a sandwich, perhaps simply dejected at his failed mission.

The driver realized his mistake and stopped to reverse. The engine stalled. The car sat motionless, five feet from Princip. The 19-year-old drew his Browning pistol and fired twice. The first shot hit Sophie in the abdomen. The second hit Franz Ferdinand in the neck. Both died within minutes.

Austria-Hungary blamed Serbia and issued an ultimatum designed to be rejected. Serbia rejected it. Austria-Hungary declared war on Serbia. Russia mobilized to support Serbia. Germany mobilized to support Austria-Hungary. France mobilized to support Russia. Germany invaded Belgium to attack France. Britain declared war on Germany.

Within six weeks of the assassination, most of Europe was at war. Within four years, 20 million were dead and four empires had fallen. All because a driver took a wrong turn, stalled his engine, and parked in front of a man with a pistol who had already given up on his mission. The corner of Franz Josef Street and Appel Quay is perhaps the most consequential intersection in human history.