It didn't. The members of the Piedmontese (and later Italian) political/ruling class had very few misgivings about seizing Rome from the Pope; indeed, it was seen as the vital last step in creating an Italian State. In the last act of the Italian Wars of, the Italian army seized Rome and annexed what remained of the Papal State on September 20, 1870.

The conquest of Rome opened up a whole bunch of cans of worms. The Pope excommunicated the House of Savoy, and in much of Italy lack of cooperation from the clergy was one of many obstacles in establishing an effectively run state. Although there were a number of complex factors at work, the Papacy's unwillingness to recognize the new Italy certainly contributed to the small but protracted insurgency in Southern Italy. Further, a whole contingent of the Roman Nobility followed the Pope in his refusal to acknowledge the Italian State; they would come to be called, "The Black Nobility." The Italian parliament would try to find a way to accomodate the Papacy as an entity operating within Italy, but none was successful until the Lateran Pacts of 1929 recognizing the Papacy's sovereignty over the Vatican City.