The Papal Schism was a political divide in the Catholic Church which lasted from 1378 to 1417. Ultimately, the situation was resolved with the Council of Constance, but not before all of the parties involved attempted violence, coercion, and of course diplomacy in an attempt to sort the matter out. This event in Western Christianity is sometimes known as the Western Schism, and less commonly as the Great Schism. Referring to the Papal Schism as the Great Schism can cause confusion with the East-West Schism which split the Western and Eastern Christian church in the 11th century.
Unlike the previous Great Schism, which was motivated by fundamental religious differences, the Papal Schism was political in nature. It had to do with the conflict between Rome, Italy and Avignon, France. Rome had been the traditional stronghold of the papacy, but in the 1300s, the papacy moved to Avignon. The French wished to retain their control of the papacy for political and prestige reasons, while the Romans demanded a return of the papacy to Italian soil.
In 1376, Pope Gregory XI moved the papacy back to Rome. Upon his death in 1378, the Romans elected Pope Urban VI. However, a group of renegade Cardinals in France were not satisfied, and they in turn elected Pope Clement VII, who came to be known as the antipope. This sparked a controversy, understandably, as two popes are not supposed to exist at once. The battle between Rome and Avignon was launched, and then confused even further in 1409, when a third pope was elected at a meeting in Pisa, Italy.
In 1417, a supporter of the third rival pope proposed the Council of Constance, a meeting which was intended to resolve the situation, determining the rightful pope and ending the Papal Schism. The Church had realized that the event was troubling for its public relations, in addition to being a bit embarrassing, and most of the parties at the council were eager to see the matter brought to an end, although they might have supported different popes.
In addition to ultimately deposing both antipopes, the Council of Constance also put forward a series of political and religious reforms. A new pope, Martin V, was elected, ending the Papal Schism and confirming Rome as the seat of the papacy. Under Pope Martin V, the authority of the papacy was solidified, cementing the idea that the Pope was the supreme authority in the Church, and that his word was law when it came to religious matters.