They called it The War.  The Great War.  The War To End All Wars.  It was touched off by two shots of a pistol.  The tangle of international alliances is easy to see in hindsight, but for the people of the time, it must have seemed insane.  The tiny little Kingdom of Serbia refused to bow to Austro-Hungarian demands after the assassination of the heir, and the Hungarian army invaded.  Serbia called on her defensive alliance with Russia and everything went to War.