Why did the popes live in Avignon, and how did it lead to three popes at once?

The popes left Rome for Avignon because of a quarrel with the king of France. The Avignon Papacy was the period from 1309 to 1376 during which seven successive popes resided in Avignon, rather than in Rome. The situation arose from the conflict between the papacy and the French crown, which ended with the death of Pope Boniface VIII after his arrest and maltreatment by agents of Philip IV of France. After the next pope, Benedict XI, died, Philip pressured a deadlocked conclave to elect the archbishop of Bordeaux as Clement V in 1305. Clement refused to move to Rome, and in 1309 he moved his court to the papal enclave at Avignon, where it remained for 67 years. All seven Avignon popes were French and all were under the influence of the French crown.

In 1376 Gregory XI abandoned Avignon, arriving in Rome in January 1377. The Avignon Papacy had developed a reputation for corruption that estranged much of Western Christendom, attributed to perceptions of strong French influence and to the papal curia's efforts to extend its powers of patronage and to raise revenues.

Then came the split. After Gregory's death, Urban VI was elected, and in September 1378 a group of French cardinals declared the election invalid because of intimidation and violence, and elected Clement VII, who claimed to be the true pope. The dissident cardinals argued that Urban's election was invalid because it had been made out of fear of the rioting Roman crowds. That was the Western Schism: bishops in Rome and Avignon each claimed to be the true pope. It was driven by international rivalries, personalities and political allegiances.

It got worse before it got better. In 1409 the Council of Pisa tried to depose both claimants but proceeded to inflame the problem by electing a third, Alexander V. The historian Johan Huizinga recorded how fierce the feeling became: in 1382 the oriflamme, a banner that might only be unfurled in a holy cause, was taken up against the Flemings because they were Urbanists, "that is, infidels".

The Council of Constance, held from 1414 to 1418, ended the schism by deposing or accepting the resignation of the remaining claimants and electing Martin V. The Catholic Church today recognizes the Roman line as the sole legitimate one.