In the early summer of 1866 half a million men from Prussia and the Austrian Empire fought the largest battle in European history prior to 1914 in the rolling hills of eastern Bohemia. The results of the battle determined that Prussia and not Austria would be paramount in the German world going forward. The Prussian victory at the Battle of Königgrätz has traditionally been ascribed to their possession of a breech-loading rifle and use of railways. This book shows that it was not technology but maneuver and traditional generalship that led to the Prussian victory. The Seven Weeks' War was Europe's first modern, technological war but has largely been consigned to the dustbin of history as both countries that fought it no longer exist. This is the story of Königgrätz. One long summer day that changed the course of history for the Germans.