Temporal power (papal)
Some historians identify the crowning of Charlemagne in 800 as the moment in which the Church started having an international importance in a modern sense, although the temporal power can be traced even earlier to either the Donation of Pepin in 754, or the crowning of Pepin by Pope Zachary in 752, the first time a secular sovereign was crowned by a pope. Charlemagne's crowning, however, was perhaps the first moment in which the Church was generally granted a power of control of the imperial dignity, thus demonstrating a sort of power of international veto. Subsequently, the Donation of Constantine was forged to provide a legal basis for the temporal power.
The temporal power was abolished by Napoleon Bonaparte, who dissolved the Papal States and incorporated Rome and Latium into his French Empire. The temporal power was restored by the Great Powers at the 1815 Congress of Vienna. The Napoleonic civil laws were abolished, and most civil servants were removed from office. Popular opposition to the reconstituted corrupt clerical government led to numerous revolts, which were suppressed by the intervention of the Austrian army.
In November 1848, following the assassination of his minister Pellegrino Rossi, Pope Pius IX fled Rome. During a political rally in February 1849, a young Roman priest, the Abbé Arduini, described the temporal power of the popes as a "historical lie, a political imposture, and a religious immorality." On 9 February 1849, the newly elected Roman Assembly proclaimed the Roman Republic. Subsequently, the Constitution of the Roman Republic abolished the temporal power, although the independence of the pope as head of the Catholic Church was guaranteed by article 8 of the "Principi fondamentali".
At the end of June 1849, the Roman Republic was crushed by 40,000 French troops sent by Louis Napoleon Bonaparte (later Napoleon III), at the urging of the rabid ultramontane French clerical party. The temporal power was restored and propped up by a French garrison.
In 1859–60, the Papal States lost Romagna, Marche and Umbria. These regions were incorporated into the Kingdom of Italy, and the temporal power was reduced to Rome and the region of Lazio. At this point, some ultramontane groups proposed that the temporal power be elevated into a dogma. According to Raffaele De Cesare:
The first idea of convening an Ecumenical Council in Rome to elevate the temporal power into a dogma, originated in the third centenary of the Council of Trent, which took place in that city in December, 1863, and was attended by a number of Austrian and Hungarian prelates.
However, following the Austro-Prussian War, Austria had recognized the Kingdom of Italy. Thus the revival of the temporal power of the pope was deemed impossible. Some suggested the solemn proclamation in an ecumenical council of the ancient  catholic teaching of papal infallibility, according to which a pope cannot err in his teaching on faith or morals when solemnly proclaimed, could make up for this loss.
On 20 September 2000, an item in the Catholic publication Avvenire stated:
That in 1970, precisely on 20 September 1970, Pope Paul VI sent Cardinal Angelo Dell'Acqua, his vicar for Rome, to Porta Pia to celebrate the "providential" significance of the loss of the temporal power. Since then, at least since then, Porta Pia has also been a Catholic celebration!
Formally, the temporal power was restored in 1929 with the treaty between the Vatican State and Italy (Concordat), when the papacy accepted to have no more interests on Italy, its closest neighbor, and therefore on any other country. Some small degree of temporal power persists in the formal government of the Vatican City as an independent state.