Italy became a nation-state belatedly - on March 17, 1861, when most of the states of the peninsula were united under king Victor Emmanuel II of the Savoy dynasty, which ruled over Piedmont. The architects of Italian unification were Count Camillo Benso di Cavour, the Chief Minister of Victor Emmanuel, and Giuseppe Garibaldi, a general and national hero. In 1866 Prussian Prime Minister Otto von Bismarck offered Victor Emmanuel II an alliance with the Kingdom of Prussia in the Austro-Prussian War. In exchange Prussia would allow Italy to annex Austrian-controlled Venice. King Emmanuel agreed to the alliance and the Third Italian War of Independence began. The victory against Austria allowed Italy to annex Venice. The one major obstacle to Italian unity remained Rome. In 1870, Prussia went to war with France starting the Franco-Prussian War. To keep the large Prussian army at bay, France abandoned its positions in Rome in order to fight the Prussians. Italy benefited from Prussia's victory against France by being able to take over the Papal State from French authority. Italian unification was completed, and shortly afterward Italy's capital was moved to Rome. Rome itself remained for a decade under the Papacy, and became part of the Kingdom of Italy only on September 20, 1870, the final date of Italian unification. The Vatican City is now, since the Lateran Treaty of 1929, an independent enclave surrounded by Italy, as is San Marino.