During the middle ages there was a period where there were a series of popes who lived in a place known as Avignon France, instead of Rome, Italy. This is known as the Avignon Papacy. The Avignon Papacy caused some conflict when it came to who should be elected as pope. The Great Western Schism began as somewhat of an outcome of the Avignon Papacy, because it had a lot to do with who to elect as Pope.
How it Began
When the College of Cardinals had to elect a pope, a large mob of Romans surrounded the building. These Romans were demanding that they wanted a Roman, or at least an Italian pope; not another French pope. The College of Cardinals did eventually end up electing a pope. They elected an Italian man named Bartolomeo Prignano, who had an even temperament. After being elected the new pope took the name of Urban VI.
Even though Urban VI was known for his temperament, this did not last long. Urban VI began acting strangely, displaying erratic behavior. For example he violently denounced Church officials who were visiting him, and he also struck one of these Church officials, which isn’t exactly proper behavior from a pope. At this point the cardinals reassembled to choose a new pope, because clearly Urban VI was not very qualified.
The cardinals then elected a Frenchman who became Clement VII. Of course Urban VI was not very happy about this and even refused to abdicate. But the cardinals firmly stated that his election was not legitimate because of all the pressure they were experiencing due to the angry mob outside of the election. After Clement VII was elected he began living in Avignon, which went against what the Romans wanted, hence this caused the Great Western Schism.
How was it Resolved
Because of the situation with the two popes Europe was in a state of confusion; different countries supported different popes. In 1409 the Council of Pisa discussed what to do; in the end they concluded that since there was so much conflict on who should be pope between Urban VI and Cement Vll, they would elect a new pope, and say that Urban and Clement were not actually popes. So in 1415, a new pope was elected, named Martin V; eventually he was acknowledged as the official pope.
Throughout the middle ages there have been many conflicts that involved the Papacy. Usually these conflicts were between a king and a pope, but the Great Western Schism is unique for it was a conflict between two popes. Like all conflicts the Great Western Schism was eventually resolved, but the Church did not take an official stance on it until much later.