The Kingdom of Italy (Italian: Regno d'Italia) was a state founded in 1861 when King Victor Emmanuel II of Sardinia was proclaimed King of Italy. The state was founded as a result of the unification of Italy under the influence of the Kingdom of Sardinia, which was its legal predecessor state. It existed until 1946 when the Italians opted for a republican constitution.
Italy declared war on Austria in alliance with Prussia in 1866: despite an unsuccessful campaign, it received the region of Veneto following Bismarck's victory. Italian troops entered Rome in 1870, ending more than one thousand years of Papal temporal power. Italy accepted Bismarck's proposal to enter in a Triple Alliance with Germany and Austria-Hungary in 1882, following strong disagreements with France about the respective colonial expansions. However, even if relations with Berlin became very friendly, the alliance with Vienna remained purely formal, as the Italian lands of Trentino and Trieste were still under Austro-Hungarian rule. So, in 1915, Italy accepted the British invitation to join the Allies in World War I because the western allies promised territorial compensation (at the expense of Austria-Hungary) for participation that were 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.
"Fascist Italy" is the era of National Fascist Party rule from 1922 to 1943 with Benito Mussolini as totalitarian leader. The fascists imposed totalitarian rule and crushed the political and intellectual opposition, while promoting economic modernization, traditional social values, and a rapprochement with the Catholic Church. "The Fascist regime passed through several relatively distinct phases," says Payne (1996). The first phase 1923–25 was nominally a continuation of the parliamentary system, albeit with a "legally organized executive dictatorship." Then came the second phase, "the construction of the Fascist dictatorship proper from 1925 to 1929." The third phase, with less activism, was 1929-34. The fourth phase, 1935–40, was characterized by an aggressive foreign policy, warfare in Ethiopia, confrontations with the League of Nations sanctions, growing economic autarchy, and semi-Nazification. The war itself (1940–43) was the fifth phase with its disasters and defeats, while the rump Salo regime under German control was the final stage (1943–45).
Italy was allied with Nazi Germany in World War II until 1943. It switched sides to the Allies after ousting Mussolini and shutting down the Fascist party in areas (south of Rome) controlled by the Allied invaders. The remnant fascist state in northern Italy that continued fighting against the Allies was a puppet state of Nazi Germany, the "Italian Social Republic", still led by Mussolini and his loyalist Fascists. Shortly after the war, civil discontent led to the Italian constitutional referendum, 1946 on whether Italy would remain a monarchy or become a republic. Italians decided to abandon the monarchy and form the Italian Republic, which is the present form of Italy today.