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How did Italy acquire Venetia in 1866?

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Unification of Italy — unification of Italy The unification of Italy. The dates are those of annexation, first to Sardinia-Piedmont and after 1861 to the Kingdom of Italy.

In 1866, Italy acquired Venetia as a result of the Seven Weeks' War between Austria and Prussia.12

Prior to the conflict, the Italian government formed an alliance with Prussia, which had promised to secure Venetia for Italy in exchange for its participation in the war against the Habsburg empire. Although Italian forces suffered military defeats against the Austrians on both land at Custoza and at sea near Lissa, the Prussian army achieved a decisive victory at the Battle of Königgrätz.21

Following the Prussian success, the war concluded with the Treaty of Prague (August 1866), which mandated that Austria cede Venetia. Through the mediation of Napoleon III, the territory was formally transferred to the Kingdom of Italy via the Treaty of Vienna on October 3, 1866.231