The Battle of Lissa (or Battle of Vis) (Croatian: Bitka kod Visa) took place on 20 July 1866 in the Adriatic Sea near the Dalmatian island of Vis (Italian: Lissa) and was a significant victory for an Austrian Empire force over a numerically superior Italian force. It was the first major sea battle between ironclads and one of the last to involve deliberate ramming. The Italian navy fired roughly 1450 shots during the engagement, but failed to sink any Austrian ship while losing two ironclads.

One of the main reasons for this poor performance was internal rivalry between the Italian fleet commanders: for example, Italian Vice Admiral Albini, with his ships, did not engage the enemy during the battle. The engagement was made up of several small battles: the main battle was between seven Austrian and twelve Italian ironclads and showed the ability of Austrian commander Tegetthoff to divide his more numerous opponents and then destroy the isolated ironclads.

The Austro-Prussian War, Seven Weeks' War, German Civil War, Brothers War or Fraternal War, known in Germany as Deutscher Krieg ("German War"), Deutscher Bruderkrieg ("German war of brothers") and by a variety of other names, was fought in 1866 between the Austrian Empire and the Kingdom of Prussia, with each also being aided by various allies within the German Confederation. Prussia had also allied with the Kingdom of Italy, linking this conflict to the Third Independence War of Italian unification. The Austro-Prussian War was part of the wider rivalry between Austria and Prussia, and resulted in Prussian dominance over the German states.

The major result of the war was a shift in power among the German states away from Austrian and towards Prussian hegemony. It resulted in the abolition of the German Confederation and its partial replacement by the unification of all of the northern German states in the North German Confederation that excluded Austria and the other Southern German states, a Kleindeutsches Reich. The war also resulted in the Italian annexation of the Austrian province of Venetia.