Along with the crises of the Black Plague which devastated much of Europe and crippled society and the 100 Years War, which cost hundreds of lives on both sides of the conflict, the Western Schism affected the Papacy and its effective rule over Christendom. It began with the Babylonian Captivity which moved the seat of Papal authority to Avignon, France rather than its traditional home in Rome. In 1309, the French King attempted to institute a tax on church income. The Pope resisted and threatened the King with excommunication. Once the current pope died, his successor was French and desired to be closer to the protection of the French monarchy (and perhaps also a mistress or two). The decline of the clergy continued unchecked while the papacy remained in Avignon, and the city and its papal holdings were referred to as Babylon by Petrarch. In Avignon, the papacy went for a policy of virtually anything goes. Ultimately Pope Clement VI spoke out against the rampant corruption and sale of church office, position and holy relics.
Understandably, it was difficult for the Pope to manage his vast landed estates in Italy from his seat in France. Revolts came from all sides – from the people of Rome who had to deal with increasing taxation to support the Pope in France and from the city-states that defined Italian governance in the late medieval period into the Renaissance. The position became more and more untenable until, finally, Pope Gregory XI was forced to return to Rome in an ultimately failed attempt to regain control. Demanding an Italian pope, Urban VI was elected. Urban attempted to reign in church corruption and institute a general reform which was not met well by the Cardinals. The French cardinals banded together and declared Urban VI’s election to be invalid. They continued on to create a conclave of their own and elected Clement VII, who was guilty of causing the massacre of over 5000 civilians in his brutal suppression of an attempted revolt. At this point, two Popes governed the church, and alliances were split between European Christian nations, although people generally followed the guidance of their own monarchs, with England typically in support of the Roman Pope and France understandably entrenched in support of the French Pope.
If two Popes were not sufficient, at one point in the Schism (ironically in trying to heal it) there were three Supreme Pontiffs at one time. When Urban VI died, instead of healing the schism in the church and recognizing the reign of Clement VII, the Roman cardinals elected a successor for Urban VI and named Boniface IX. Similarly, upon the death of Clement VII, the French cardinals elected his successor Benedict XIII. The council of Pisa was called to resolve the schism and decide on a single Pope to unite the church. Neither of the current Popes chose to attend, and the cardinals deposed them both, electing instead Alexander V. This created three rival papacies, throwing the church in to further disarray. A second council was called at Constance. In addition to removing the problem of the schism, the council aimed to address church reforms and to remove the threats of heresy springing up from the disjointed church leadership. The council, after deposing 3 Popes for the price of one (and after granting themselves the power to do so) elected Martin V, which ultimately ended the Western Schism and once again united the church. Understandably, the problems and upheaval created by the schism at the highest orders of church leadership fed directly into the desire for reformation, and provided the breeding ground necessary for the upcoming Protestant reformation to take root.
Photo Credit: By Jean-Marc Rosier from http://www.rosier.pro, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4837750