Before the Protestant Reformation of the early 16th century, there had been another major split in the Christian church. Instead of a number of sects forming to protest (hence the name “protestant”) the Catholic (universal) church, the great schism was a split between the traditional Roman Catholic church and the Eastern Orthodox (most commonly, the Greek Orthodox) church. The reasons for the split are many and varied. While many claim the reason was interpretation of divine law, equally as many would state the reason for the split was political.
Depending on who one gets his information from, the great schism started as early as 1054. The West (Roman Catholic) was seen as taking on great political, as well as ecumenical, power. The East (Greek Orthodox) saw this as over-reaching the bounds of the church. Symbolically, Pope Leo IX and Patriarch Michael Cerularius excommunicated each other. Though this symbolic act affected few in the church, it was symptomatic of the split to come. As the next three centuries passed, the divide between East and West became more pronounced.
More than one attempt at reconcilliation was made to bring East and West back together, but tensions grew more and more cold. During the fourth crusade, Constantinople was sacked and any hope of reconcilliation was effectively defeated.
There was, however, another great schism within the Western (Roman Catholic) side of the Christian church. Again, depending on whom one listened to, there was a short time when there were two and even three different popes.
After the death of Pope Gregory XI, the cardinals elected Pope Urban VI. The idea behind this move was to bring the papacy back to an Italian, as the church had grown more and more influenced by the French, having the pope housed at Avignon. However, after electing Urban, the cardinals realized their mistake. Urban ruled with an iron fist and was considered by many downright dictatorial.
Many of the French cardinals decided to hold another papal election, declaring the first null and void. This was based on claims of extortion during the first election, in which several cardinals claimed to have had their lives threatened. A new pope was elected (Clement VII), though he was only recognized by the “Avignon” line. The “Roman” line still viewed Urban as their leader. For the better part of the next thirty years, there were, within the West, effectively two Roman Catholic churches.
In 1409, the Council of Pisa convened and effectively dethroned both of the sitting popes (Gregory XII from Rome and Benedict XIII from Avignon). A third, and by now effectively only, pope was elected (Alexander V) and the western (Roman Catholic) church was considered unified again. Shortly after Alexander, Pope John XXIII took over and, though considered brutal in his own way, did manage to effectively unify the church.
Though the Western church is still considered one entity, the great schism still exists today, as Roman Catholics and Eastern Orthodox churches both claim divine right.