Third Italian War of Independence

The Third Italian War of Independence was fought in 1866, when the Kingdom of Italy allied itself with Prussia against Austria at the outset of the Austro-Prussian War, hoping to gain the still-Austrian-held region of Venetia. Italian forces suffered defeat on both land and sea, losing the Battle of Custoza to Austrian troops and the naval Battle of Lissa in the Adriatic despite fielding a larger fleet, embarrassing setbacks that stood in sharp contrast to Prussia's decisive victory over Austria on the northern front. Because Prussia's success forced Austria to make peace regardless of the fighting in Italy, the Treaty of Vienna in October 1866 still ceded Venetia to Italy, allowing the kingdom to complete most of its territorial unification despite its own poor military performance in the war.