In 1866 Austria and Prussia fought the Austro-Prussian War or Seven Weeks War. Overtly fought over control of Schleswig-Holstein, the war brought to a head the rivalry between Otto von Bismarck's vision of a Prussian-dominated Kleindeutschland and the Austrian alternative of a pan-Germanic Grossdeutschland. Prussian élan and organisation quickly crushed Austria, leaving Bismarck's state dominant in Central Europe.

The war was decided in the Battle of Königgratz on July 3 and paved the way for the Prussia-led German Empire of 1871.