Papacy
The office of the bishop of Rome, for a thousand years the only universal authority in Europe and still a sovereign state with global reach.
For most of European history there was exactly one institution that claimed authority over every kingdom without being contained by any of them. Kings ruled territory. The bishop of Rome claimed to rule souls, everywhere, and for several centuries he could make a king kneel in the snow to prove it. The papacy is the longest continuously functioning institution in the Western world, and understanding European politics before 1500 is largely a matter of understanding what it could and could not compel.
The claim
The claim rests on a passage in Matthew's gospel in which Jesus tells Peter that he is the rock on which the church will be built and gives him the keys of the kingdom. Peter was traditionally held to have died in Rome, so his successors as bishop of Rome inherited the primacy. Other claims were manufactured. The Donation of Constantine, a document purporting to record the emperor's gift of imperial authority over the West to the pope, underpinned papal territorial claims for seven hundred years until the humanist Lorenzo Valla demonstrated in 1440 that its Latin was centuries too late to be genuine.
Pope as king
From 756, when the Frankish king Pepin handed over a swath of central Italy, the pope was also a territorial monarch. The Papal States survived until Italian troops took Rome in 1870. This dual identity, universal pastor and Italian prince, is the source of most of the institution's political trouble. It made popes into combatants with armies, treasuries, and nephews to provide for.
The high point of papal power was the eleventh and twelfth centuries. In the Investiture Controversy, Gregory VII asserted that only the pope could appoint bishops and that he could depose emperors. When Henry IV of Germany defied him, Gregory excommunicated him and released his subjects from their oaths, and in 1077 Henry stood outside the castle at Canossa in the snow for three days waiting for absolution. Innocent III, a century later, arbitrated who would be emperor, placed England under interdict until its king submitted, and launched the Fourth Crusade.
The long fall
The descent was equally instructive. From 1309 the popes lived at Avignon under French influence. Then came the Great Schism of 1378 to 1417, when rival popes in Rome and Avignon excommunicated each other and, for a while, a third claimant joined in, so that all of Latin Christendom was under somebody's anathema. A council, not a pope, resolved it, which raised a question about where authority really lay that the Reformation would ask again with force in 1517.
By 1870 the pope had lost his territory entirely and responded by refusing to leave the Vatican. Successive popes were voluntary prisoners for fifty-nine years, until the Lateran Treaty of 1929 with Mussolini created Vatican City, a sovereign state of about a fifth of a square mile.
Power without divisions
Stalin is supposed to have asked how many divisions the pope had. The answer was none and it did not settle the matter. When John Paul II, a Pole, visited Poland in June 1979, millions turned out and discovered how many of them there were. The Solidarity movement began fourteen months later. The Holy See maintains diplomatic relations with around 180 states and permanent observer status at the United Nations, the only religious body seated among governments. The succession still works the way it always has: when Francis died in April 2025 after twelve years, the conclave chose Robert Prevost, an American cardinal who had spent decades as a missionary and bishop in Peru, and he took the name Leo XIV, the 267th holder of the office and the first from the United States. It is the last working example of an authority that is genuinely transnational because it never accepted the terms of the territorial state in the first place.