Capture of Rome in the context of "Camillo Benso, Count of Cavour"

The Unification of Italy (Italian: Unità d'Italia [uniˈta ddiˈtaːlja]), also known as the Risorgimento (Italian: [risordʒiˈmento]; lit. 'Resurgence'), was the 19th century political and social movement that in 1861 ended in the annexation of various states of the Italian peninsula and its outlying isles to the Kingdom of Sardinia, resulting in the creation of the Kingdom of Italy. Inspired by the rebellions in the 1820s and 1830s against the outcome of the Congress of Vienna, the unification process was precipitated by the Revolutions of 1848, and reached completion in 1870 after the capture of Rome and its designation as the capital of the Kingdom of Italy.

Individuals who played a major part in the struggle for unification and liberation from foreign domination included King Victor Emmanuel II; politician, economist and statesman Camillo Benso, Count of Cavour; general Giuseppe Garibaldi; and journalist and politician Giuseppe Mazzini. Borrowing from the old Latin title Pater Patriae of the Roman emperors, the Italians gave to King Victor Emmanuel II the epithet of Father of the Fatherland (Italian: Padre della Patria). Even after 1870, many ethnic Italian-speakers (Italians in Trentino-Alto Adige/Südtirol, Savoyard Italians, Corfiot Italians, Niçard Italians, Swiss Italians, Corsican Italians, Maltese Italians, Istrian Italians, and Dalmatian Italians) remained outside the borders of the Kingdom of Italy, planting the seeds of Italian irredentism.

The Kingdom of Italy (Italian: Regno d'Italia, pronounced [ˈreɲɲo diˈtaːlja]) was a unitary state that existed from 17 March 1861, when Victor Emmanuel II of Sardinia was proclaimed King of Italy, until 10 June 1946, when the monarchy was abolished, following civil discontent that led to an institutional referendum on 2 June 1946. This resulted in a modern Italian Republic. The kingdom was established through the unification of several states over a decades-long process, called the Risorgimento. That process was influenced by the Savoy-led Kingdom of Sardinia, which was one of Italy's legal predecessor states. In 1882 it became a colonial empire, establishing the Italian Empire.

In 1866, Italy declared war on Austria in alliance with Prussia and, upon its victory, received the region of Veneto. Italian troops entered Rome in 1870, ending more than one thousand years of Papal temporal power. In the last two decades of the 19th century, Italy developed into a colonial power, and in 1882 it entered into a Triple Alliance with the German Empire and the Austro-Hungarian Empire, following strong disagreements with France about their respective colonial expansions. Although relations with Berlin became very friendly, the alliance with Vienna remained purely formal, due in part to Italy's desire to acquire Trentino and Trieste from Austria-Hungary. As a result, Italy accepted the British invitation to join the Allied Powers during World War I, as the western powers promised territorial compensation (at the expense of Austria-Hungary) for participation that was more generous than Vienna's offer in exchange for Italian neutrality. Victory in the war gave Italy a permanent seat in the Council of the League of Nations, but it did not receive all the territories it was promised.

The Holy See exercised temporal power, as distinguished from its spiritual and pastoral activity, while the pope ruled the Papal States in central Italy. The Papal States ceased to exist following the capture of Rome in 1870 by the Royal Italian Army, after which its remaining territories were annexed to the Kingdom of Italy. The Lateran Treaty of 1929 later established the Vatican City, a small city-state where the Holy See currently exercises temporal powers.

Pope Pius IX (Italian: Pio IX; born Giovanni Maria Battista Pietro Pellegrino Isidoro Mastai-Ferretti; 13 May 1792 – 7 February 1878) was head of the Catholic Church from 1846 to 1878. His reign of nearly 32 years is the longest verified of any pope in history and second only to Saint Peter according to Catholic tradition. He was notable for convoking the First Vatican Council in 1868 which defined the dogma of papal infallibility before taking a break in summer of 1870. The council never reconvened. At the same time, France started the French-Prussian War and removed the troops that protected the Papal States, which allowed the Capture of Rome by the Kingdom of Italy on 20 September 1870. Thereafter, he refused to leave Vatican City, declaring himself a "prisoner in the Vatican".

At the time of his election, he was a liberal reformer, and during his early papacy, he enacted progressive reforms, but his approach changed after the Revolutions of 1848. When his prime minister, Pellegrino Rossi, was assassinated and Pius himself was made prisoner in his own palace, he fled Rome and excommunicated all participants in the short-lived Roman Republic. After its suppression by the French army and his return in 1850, his policies and doctrinal pronouncements became increasingly conservative. He was responsible for the kidnapping of Edgardo Mortara, a six-year-old taken by force from his Jewish family who went on to become a Catholic priest in his own right and unsuccessfully attempted to convert his Jewish parents.

The First Ecumenical Council of the Vatican, commonly known as the First Vatican Council or Vatican I, was the 20th ecumenical council of the Catholic Church, held three centuries after the preceding Council of Trent which was adjourned in 1563. The council was convoked by Pope Pius IX on 29 June 1868, under the rising threat of the Kingdom of Italy encroaching on the Papal States. It opened on 8 December 1869 and was adjourned on 20 September 1870 after the Italian Capture of Rome. Its best-known decision is its definition of papal infallibility.

The council's main purpose was to clarify Catholic doctrine in response to the rising influence of the modern philosophical trends of the 19th century. In the Dogmatic Constitution on the Catholic Faith (Dei Filius), the council condemned what it considered the errors of rationalism, anarchism, communism, socialism, liberalism, materialism, modernism, naturalism, pantheism, and secularism.

The Anniversary of the Unification of Italy (Italian: Anniversario dell'Unità d'Italia) is a national day that falls annually on 17 March and celebrates the birth of Italy as a modern nation state, which took place following the proclamation of the Kingdom of Italy on 17 March 1861.

However, the complete unification of Italy took place only in the following years. In 1866 the Veneto and the province of Mantua were annexed after the Third Italian War of Independence, then in 1870 Lazio after the capture of Rome, and finally in 1918 Trentino-Alto Adige and Julian March after the First World War. In this regard, the National Unity and Armed Forces Day (Victory Day) was also established, which is celebrated annually on 4 November, recalling the Italian victory in the First World War, a war event considered to complete the process of unification of Italy.