The Great Schism
It began 20 September 1378 when a majority of the cardinals, having declared their election of the Neapolitan Bartolomeo Prignano (Urban VI) 5 months previously to be invalid because of the undue pressure exerted by the Roman mob, elected the Frenchman Robert of Geneva (Clement VII). Although the schism was caused by acute personal differences between Urban and the cardinals, most of whom, being Frenchmen, were deeply unhappy over the return of the Papacy from Avignon to Rome, Christendom divided along political lines once the double election had taken place, with France and her allies Aragon, Castile and Scotland supporting Clement, while England, the Emperor and most other princes remained loyal to Urban.
Most of the Italian states stood behind Urban but in Naples Queen Giovanna I of Anjou provoked a popular and baronial revolt by sheltering Clement, and for the next 20 years the kingdom was contested between, on one side, Charles III of Durazzo (d. 1386) and his son Ladislas, who recognized the Roman pope, and, on the other, Louis I (d. 1384) and Louis II of Anjou, who had the support of the Avignon pope. In northern Italy, the scene was dominated by the expansionist policies of Giangaleazzo Visconti of Milan until his death in 1402; from time to time both he and his opponents, the Florentines, flirted with the Avignon popes in the hope of obtaining French support, but with little effect.
Meanwhile the temporal power of the Roman popes survived despite Urban's gift for quarrelling with all his allies, and was considerably built up by his able successor Boniface IX (1389-1404). However, on his death the Roman papacy fell under the domination of King Ladislas of Naples, who drove north through Rome to threaten central Italy, causing the Florentines and most of the other Italian states to throw their weight behind a group of cardinals from both camps who met at Pisa and elected a third pope, Alexander V, in June 1409. It was the continued pressure of Ladislas that finally compelled Alexander's successor Baldassare Cossa (John XXIII) to summon the Council of Constance (1414-18}. This Council healed the Schism by deposing both John and the Avignon pope Benedict XIII and accepting the resignation of the Roman pope, thus leaving the way open for the election in 1417 of Martin V (1417-31), who set about the task of restoring the shattered power and prestige of the Holy See. The 39-year schism killed the supranational papacy of the Middle Ages, for; while devout Christians agonized, practical politicians (often the same people) seized the chance to extend their jurisdiction at the Church's expense. As a result, the Renaissance popes were much more dependent on their Italian resources, and therefore far more purely Italian princes, than their medieval predecessors.