The Kingdom of Italy (Italian: Regno d'Italia, pronounced [ˈreɲɲo diˈtaːlja]) was a unitary state that existed from 17 March 1861, when Victor Emmanuel II of Sardinia was proclaimed King of Italy, until 10 June 1946, when the monarchy was abolished, following civil discontent that led to an institutional referendum on 2 June 1946. This resulted in a modern Italian Republic. The kingdom was established through the unification of several states over a decades-long process, called the Risorgimento. That process was influenced by the Savoy-led Kingdom of Sardinia, which was one of Italy's legal predecessor states. In 1882 it became a colonial empire, establishing the Italian Empire.
In 1866, Italy declared war on Austria in alliance with Prussia and, upon its victory, received the region of Veneto. Italian troops entered Rome in 1870, ending more than one thousand years of Papal temporal power. In the last two decades of the 19th century, Italy developed into a colonial power, and in 1882 it entered into a Triple Alliance with the German Empire and the Austro-Hungarian Empire, following strong disagreements with France about their respective colonial expansions. Although relations with Berlin became very friendly, the alliance with Vienna remained purely formal, due in part to Italy's desire to acquire Trentino and Trieste from Austria-Hungary. As a result, Italy accepted the British invitation to join the Allied Powers during World War I, as the western powers promised territorial compensation (at the expense of Austria-Hungary) for participation that was more generous than Vienna's offer in exchange for Italian neutrality. Victory in the war gave Italy a permanent seat in the Council of the League of Nations, but it did not receive all the territories it was promised.