Italien fanns inte före 1929

Italian unification
Main article: Roman Question
View of the dome of Saint Peter's Basilica from Borgo Santo Spirito.

In 1870, the Pope's holdings were left in an uncertain situation when Rome itself was annexed by the Piedmont-led forces which had united the rest of Italy, after a nominal resistance by the papal forces. Between 1861 and 1929 the status of the Pope was referred to as the "Roman Question". In 1871, the Palazzo Quirinale, for centuries the Papal palace, was confiscated by the king of Italy and became the royal palace. Thereafter the popes resided undisturbed within the Vatican walls, and certain papal prerogatives were recognized by the Law of Guarantees, including the right to send and receive ambassadors. But the Popes did not recognise the Italian king's right to rule in Rome, and they refused to leave the Vatican compound until the dispute was resolved in 1929. Other states continued to maintain international recognition of the Holy See as a sovereign entity.

In practice Italy made no attempt to interfere with the Holy See within the Vatican walls. However, they confiscated church property in many other places, including, perhaps most notably, the Quirinal Palace, formerly the pope's official residence. Pope Pius IX (1846–78 ) , the last ruler of the Papal States, claimed that after Rome was annexed he was a "Prisoner in the Vatican".