In a shocking move, Pope Benedict XVI announced that, effective February 28th, he will resign due to the frailty caused by his age. This news surprised the cardinals and started the frenzied speculations about his successor.
The last time a pope resigned took place in 1415 when Pope Gregory XII died so to end the Western Schism. For those without the ability to time travel and those not as old as the Czar or Volgi, After Pope Gregory XI died, the cardinals elected Pope Urban VI. Shortly after that they became concerned with his attitude and temperament, they left Rome and relocated in Anagni where they elected Pope Clement VII. Various parts of the world chose one side of the schism or the other. France, Aragon, Castile, Leon, Cyprus, Burgundy, Savoy, Naples and Scotland favored the Avignon papacy of Pope Clement VII. Denmark, England, Flanders, Venice, the Holy Roman Empire, Hungary, Ireland, Norway, Poland, Sweden and northern Italy all backed the papacy of Pope Gregory XII.
This schism continued for over 30 years and expanded when an attempt to reconcile the schism during a church council held in Pisa in 1409 only resulted in a third antipope, Alexander V. Alexander V was quickly succeeded by John XXIII. In 1414, the Council of Constance worked to resolve the issue and succeeded in having the Pisan antipope of the time, John XXIII, and the Roman line’s Gregory XII. The council excommunicated the Avignon antipope Benedict XIII. While the Avignon line continued until 1429, this effort essentially ended the Western Schism.
So it will be an interesting next few weeks (hopefully) as a new pope is elected to succeed Pope Benedict XVI.