After the death of Pope Gregory XI, a conclave assembled on 7 April 1378 to choose a new pope.  This conclave was the first since the transfer of the papal see from Avignon to Rome after the end of what was known as the Babylonian Captivity of the Papacy.  It was also one of the shortest in the history of the Catholic Church – lasting only until the 9th of April and the first to be held in the old basilica of Saint Peter.

The conclave would meet under pressure and violence from Roman citizenry who demanded an Italian pope after the decades of French dominance during the Avignon Papacy.  Eventually Bartolommeo Prignano, the Archbishop of Bari, would be elected as pope, taking the name of Urban VI.

However by September, frustration over the leadership of Pope Urban would lead thirteen cardinals to claim that their votes for Urban had been coerced by the threats of the Roman mob and were, therefore invalid. Thus they held a new conclave in Fondi and elected Robert of Geneva, the anti-pope Clement VII as a rival pope.  This marked the beginning of the Western Schism – a period of multiple claimants to the papacy that would last until 1417 and the election of Pope Martin V.

For more on the Western Schism
Also listen to episode #155 of Catholic:Under The Hood