On June 28 1914, Gavrilo Princip was hanging around outside Moritz Schiller’s delicatessen in Sarajevo. In some versions of the story, he had gone there to buy a sandwich (or some kind of roll, anyway). He was at a loose end. That morning, the 19-year-old Bosnian Serb and six other would-be assassins had failed to kill the Austrian archduke Franz Ferdinand.

Suddenly, quite by chance – a crucial factor in almost any assassination – the archduke’s car appeared in front of Schiller’s. The driver had taken a wrong turn into Franz Joseph Street. Princip shot the archduke. Within weeks, the first world war had broken out.

As the author David Winner muses: “No Russian revolution, Holocaust or European Union if only Princip had fancied a pizza.” Of course, all those things (and the euro) might have happened anyway. Still, assassinations and political executions – as the recent deaths of Osama bin Laden and Colonel Muammer Gaddafi remind us – provide some of the most memorable scenes in history. Assassinations are rare occasions when the fate of nations can seem to hang on a sandwich, a briefcase or a roll of fat – in other words, on chance.