Pope Gregory X in the context of "1268–1271 papal election"

A conclave is a gathering of the College of Cardinals convened to appoint the pope of the Catholic Church. Catholics consider the pope to be the apostolic successor of Saint Peter and the earthly head of the Catholic Church.

Concerns around political interference led to reforms after the interregnum of 1268–1271 and Pope Gregory X's decree during the Second Council of Lyons in 1274 that the cardinal electors should be locked in seclusion cum clave (Latin for 'with a key') and not permitted to leave until a new pope had been elected. Conclaves are now held in the Sistine Chapel of the Apostolic Palace in Vatican City.

The Second Council of Lyon was the fourteenth ecumenical council of the Roman Catholic Church, convoked on 31 March 1272 and convened in Lyon, Kingdom of Arles (in modern France), in 1274. Pope Gregory X presided over the council, called to act on a pledge by Byzantine emperor Michael VIII to reunite the Eastern church with the West. The council was attended by about 300 bishops, 60 abbots and more than a thousand prelates or their procurators, among whom were the representatives of the universities. Due to the great number of attendees, those who had come to Lyon without being specifically summoned were given "leave to depart with the blessing of God" and of the Pope. Among others who attended the council were James I of Aragon, the ambassador of the Emperor Michael VIII Palaiologos with members of the Greek clergy and the ambassadors of Abaqa Khan of the Ilkhanate. Thomas Aquinas had been summoned to the council, but died en route at Fossanova Abbey. Bonaventure was present at the first four sessions but died at Lyon on 15 July 1274. As at the First Council of Lyon, Thomas Cantilupe was an English attendee and a papal chaplain.

In addition to Aragon, which James represented in person, representatives of the kings of Germany, England, Scotland, France, the Spains and Sicily were present, with procurators also representing the kingdoms of Norway, Sweden, Hungary, Bohemia, Poland, and the "realm of Dacia". In the procedures to be observed in the council, for the first time the nations appeared as represented elements in an ecclesiastical council, as they had already become represented in the governing of medieval universities. This innovation marks a stepping-stone towards the acknowledgment of coherent ideas of nationhood, which were in the process of creating the European nation-states.

The Treaty of Orléans was a marriage treaty signed in 1275, that led to a short-lived personal union between the kingdoms of Navarre and France. It was signed by Philip III of France and his cousin Blanche of Artois, mother and regent to the two-year-old Joan I of Navarre. The original intent of the treaty was to not create a personal union, however, but to enable Philip to administer Navarre in Joan's name. Joan was also to marry either Philip's firstborn and heir apparent, Louis, or his second son, Philip. Pope Gregory X explicitly stated that he preferred a match with the younger son, as he probably wished to avoid merging Navarre with France. Louis died in 1276, however, leaving Philip as the only choice per the terms of the treaty.

Notably, the treaty bound both Philip and Blanche to convince their children to accept the marriage once they reach the age of consent, "unless serious illness, deformity, or other reasonable impediment appears in either of them before their marriage". The treaty also stipulated that if Joan's husband was not to succeed to the French throne, she would be assigned an additional annual revenue of 4,000 livres as compensation for her dower. If Joan's husband did succeed Philip, Philip promised that she would receive an even larger dower. The treaty was to have no effect on Blanche's guardianship over Joan or Blanche's own dower. The first French-appointed governor of Navarre, per the terms of the treaty, was the seneschal of Toulouse Eustache de Beaumarché.