The schism began with a disputed election. In 1378, with a Roman crowd outside demanding an Italian pope after seventy years of French popes at Avignon, the cardinals elected Urban VI. His conduct in office alarmed them quickly, and within months the same cardinals declared the election void as made under duress and elected Clement VII, who withdrew to Avignon. Both men had been chosen by the same electors in the same year.
Europe divided along the lines of existing alliance. France, Castile, Aragon, Scotland and Naples followed Avignon; England, the Empire, Hungary, Poland and much of Italy followed Rome. Each obedience had its own curia, its own appointments and its own taxation, and religious orders split down the middle. Saints of unquestioned holiness are found on both sides, which is itself instructive: Catherine of Siena supported Rome and Vincent Ferrer supported Avignon, and no one at the time could tell from sanctity which line was valid.
An attempt to solve it made it worse. A council at Pisa in 1409 deposed both claimants and elected a third, and neither of the deposed accepted the sentence, so there were three. The knot was finally cut at Constance, which secured one resignation, deposed the other two and elected Martin V in 1417, ending the schism after thirty-nine years.