After Pope Pius IX fled Rome in late 1848, revolutionaries proclaimed the Roman Republic. French troops intervened and, after a siege, entered Rome on 1849-07-03, restoring the pope’s temporal (territorial) government. The episode showed that the Papal States could survive only with strong foreign protection, especially from France.
Pius IX returned to Rome in 1850 after French forces had restored his authority. A French garrison remained in Rome for years, acting as a deterrent against Italian nationalists who wanted to make Rome the capital of a unified Italy. This arrangement turned Rome into a long-running diplomatic problem between France, the papacy, and the Italian national movement.
The Franco-Sardinian war against Austria in 1859 encouraged uprisings across central Italy, including in the Papal Legations (the northern Papal States). These revolts weakened papal territorial control outside Rome and signaled that unification politics could spread into papal lands. The papacy and Catholic powers increasingly relied on diplomacy—and sometimes military force—to limit territorial losses.
On 1859-07-11, Napoleon III and Emperor Franz Joseph met at Villafranca and reached an armistice to end the 1859 war. The settlement floated the idea of an Italian confederation presided over by the pope, reflecting how the Papal States still mattered in Europe’s balance-of-power diplomacy. The plan did not stop the unification drive, but it shows how foreign governments tried to solve “Italy” while keeping the pope’s temporal role.
As papal provinces broke away and aligned with Piedmont-Sardinia, Pius IX used spiritual penalties to defend his territorial rights. On 1860-03-26 he issued apostolic letters excommunicating those he held responsible for revolutionary uprisings in papal territories. This step highlighted a central tension of unification: the pope combined religious authority with a claim to sovereign statehood.
On 1860-09-18, Sardinian forces defeated the Papal States’ field army at the Battle of Castelfidardo. The loss made it difficult for the Papal States to defend the Marche and Umbria and accelerated their annexation to the expanding Italian kingdom. Diplomatically, the battle narrowed the papacy’s territorial base to the area around Rome and Latium.
On 1861-03-27, the new Italian Parliament declared Rome the capital of Italy, even though the government could not yet control the city. A French garrison still protected papal rule in Rome, forcing Italian leaders to postpone direct action and rely on diplomacy and timing. This created the “Roman Question”: how could Italy unify while the pope still ruled a state inside the peninsula?
On 1864-09-15, Italy and France signed the September Convention. France agreed to withdraw its troops from Rome within two years, while Italy pledged to respect the pope’s remaining territory and avoid entering Rome. The deal was a diplomatic compromise that reduced direct French protection and increased pressure on the Papal States to find new security arrangements.
On 1864-12-08, Pius IX issued the encyclical Quanta cura together with the Syllabus of Errors. These texts condemned a range of ideas linked to modern liberal politics and church–state separation, sharpening Catholic opposition to parts of the unification program. The documents mattered diplomatically because they influenced Catholic opinion across Europe and complicated governments’ efforts to reconcile national unity with papal independence.
On 1868-02-29, a decree associated with the phrase Non expedit encouraged Italian Catholics not to take part in national parliamentary elections (“neither elector nor elected”). The policy aimed to avoid legitimizing a kingdom that had taken papal territories and still claimed Rome as its capital. It also shaped domestic politics by limiting Catholic participation while the Vatican pursued its position through diplomacy and international opinion.
The First Vatican Council opened in Rome on 1869-12-08, convened by Pius IX while the Kingdom of Italy continued to press the question of Rome. Holding a major council in the papal capital underlined the pope’s claim to independent authority and helped rally global Catholic support. The council’s timing also shows how religious decisions and diplomatic survival were intertwined for the Papal States.
When the Franco-Prussian War began in 1870, France could no longer prioritize a large protective presence in Rome. The weakening or removal of the French garrison eliminated the main military barrier that had kept Italy from taking the city. This shift shows how events outside Italy—European great-power wars—directly shaped Vatican diplomacy and the fate of the Papal States.
On 1870-09-20, Italian troops attacked and broke through Rome’s Aurelian Walls near Porta Pia, forcing papal forces to capitulate. A plebiscite followed in early October, and Rome and Latium were annexed to the Kingdom of Italy. This ended the Papal States as a territorial state and made Vatican diplomacy focus on securing independence without broad territory.
The First Vatican Council was effectively stopped on 1870-09-20, the same day Rome was taken by Italian forces. The interruption linked a major doctrinal moment of the Catholic Church to the collapse of papal temporal power. In practice, the papacy now faced the problem of maintaining diplomatic independence while surrounded by the Italian state.
On 1870-10-02, a plebiscite was held to ratify the incorporation of Rome and surrounding territory into the Kingdom of Italy. The vote helped Italy present annexation as a legal, popular decision rather than only a military conquest. For the Holy See, it marked a diplomatic defeat: the pope rejected the loss of sovereignty even as the new political reality solidified.
On 1871-05-13, Italy passed the Law of Guarantees, offering the pope personal inviolability, certain diplomatic rights, and use of key palaces, aiming to stabilize church–state relations after unification. Pius IX refused to accept the law because it was granted by the very state that had taken papal territory, and he declared himself a “prisoner of the Vatican.” The refusal left the Roman Question unresolved and defined Vatican diplomacy for decades after 1870.
Role of the Papal States and Vatican Diplomacy during Unification (1849–1870)