Short answers, pulled from the story.
Francesco Petrarca wrote the famous patriotic song called Italia mia in 1344. This work marked one of the earliest expressions of Italian national sentiment among intellectual elites rather than the general populace.
Giuseppe Mazzini formed the revolutionary patriotic Young Italy society in 1832. He reconstituted it in 1839 after its breakup with intentions to gain support from workers' groups.
The Treaty of Saint-Germain-en-Laye signed on the 10th of September 1919 allowed annexation of Trentino Alto-Adige Julian March Istria Kvarner Gulf and Dalmatian city Zara. These territorial gains were part of the agreement ending hostilities between Italy and Austria-Hungary.
Enrico Corradini founded the Italian Nationalist Association in Florence in 1910. The organization emphasized martial heroism total sacrifice of individualism equality to nation discipline obedience grandeur power of ancient Rome need for people to live dangerously.
Benito Mussolini seized power as Prime Minister of Italy in 1922 developing fascist totalitarian state involving appeal to nationalism seeking expansion via irredentist claims based on Roman Venetian empire legacies.
The Treaty of Paris was signed in 1947 which led to all territorial claims being abandoned by Italian Republic making irredentist movement vanish from politics. This treaty followed World War II and preceded the signing of the Treaty of Osimo in 1975.