June 28, 2014, will mark the 100th anniversary of what is arguably the most eventful terrorist attack in history. That was the day that Gavrilo Princip, a Bosnian Serb, shot and killed the heir to the Austro-Hungarian throne.

In one of those mega-oversimplifications that journalists love and historians abhor, the murder of the Archduke Franz Ferdinand and his pregnant wife, Sophie, led directly and unavoidably to World War I. Between 1914 and 1918, 37 million soldiers and civilians were injured or killed. If there should ever...