The unification of Italy was accomplished largely at the pope's expense. The Papal States, a territory across central Italy that the papacy had ruled since the eighth century, were annexed in 1860 apart from Rome and its surroundings, which a French garrison protected. When France withdrew during the war of 1870, Italian troops breached the wall at Porta Pia on 20 September and took the city, and Rome became the capital of the kingdom.
Pius IX refused every accommodation. He rejected the Law of Guarantees passed by the Italian parliament in 1871, which offered him personal inviolability, the use of the Vatican and Lateran palaces and an annual payment, on the ground that a right granted by a parliament could be withdrawn by one; he declined the money for the rest of his life; and he declared himself a prisoner. The instruction known as the non expedit forbade Italian Catholics to stand or vote in national elections, which kept a large part of the population out of political life for a generation.
David Kertzer's account, built from the Vatican and Italian state archives, shows how far the quarrel went beyond gesture: the popes lobbied the Catholic powers for the restoration of their territory, and the Italian government treated the papacy as a hostile power inside its own capital. Three popes lived and died without leaving the Vatican, and the standoff lasted fifty nine years.