This summer, President Obama was often golfing. Hillary Clinton and Donald Trump were promising to let the world be. The end of summer seemed sleepy, the world relatively calm. The summer of 1914 in Europe also seemed quiet. But on July 28, Archduke Franz Ferdinand of Austria was assassinated in Sarajevo by Gavrilo Princip with help from his accomplices, fellow Serbian separatists. That isolated act sparked World War I.