On July 3rd, 1866 a Prussian army overwhelmed and defeated an Austrian army near the fortress city of Koniggratz in a bloody battle that lasted all day. At a stroke, the foremost power in Germany and central Europe had been reduced to a second rate player. The event caused anxiety and alarm in the capitals of the western world. How was an upstart country like Prussia able to upset the balance of power in Europe? Only sixteen years before it had been put in its place by Austria with the treaty of Olmutz. Its performance as an Austrian ally had been less than stellar in the 2nd Schleswig War of...