Austria challenged Count Otto von Bismarck's Prussian political schemes in Europe and his secret alliances with France and Italy. Many of the southern German states agreed and war became inevitable as Bismarck mobilised Prussia against Austria. Italy also declared war on Austria.
The pattern of this short war was one of military success of Prussia over Austria, particularly at Koniggratz, but of Austrian success over Italy at Custozza and Lissa (an interesting ironclad naval battle) but ultimately the French Napoleon III offered mediation and the Treaty of Prague excluded Austria from German affairs and gave back Italy her losses.

• Custozza 24 June 1866
• Koniggratz (or Sadowa) 03 July 1866
• Lissa (Vis) 20 July 1866