Excerpts from Books and Wikipedia
"The choice of the conclave fell on the archbishop of Bari, who took the title of Urban VI, but within a short time a majority of the cardinals had second thoughts. The new pope was proving too harsh a disciplinarian for their taste, and on September 20, 1378, they elected another pope, Clement VII, claiming that the first election had been held under duress. There were now two popes, one based in Rome and the other at Avignon, where Clement VII set up court. This unprecedented situation caused lasting damage to the reputation of the Church as well as to the papacy." [Furtado: 1001 Days]