The Great Schism can refer to two separate events. The first is the East-West Schism of 1054. The second is the Western Schism of 1378-1417.

The effects of the Great Schism of 1054 had a profound impact on the entire history of the Catholic Church. It definitively set Rome as the central location of Catholic authority with the Pope as the Church's leader. It resulted in the permanently separate church hierarchy and ecclesiastical practices between the Catholic Church and Eastern Orthodox Christianity. An immediate effect was that Italy was left vulnerable to attacks by the Normans. Pope Leo IX had hoped to form a common military alliance against the Normans, but the division meant that aid from the east never arrived. This led to the establishment of several Norman fiefdoms in Italy, which eroded the power of the Papacy for some time.

Feuds, some of them violent and deadly, occurred between Catholics and Eastern Orthodox Christians throughout the High Middle Ages. This includes the Massacre of the Latins in 1182 and the pillaging of Constantinople in 1204. In 1965, a nominal attempt at reconciliation between the two churches was made. To this day, each church sends a delegation to the other's celebration of their patronal feast. However, deep divides still exist which will likely never be rectified.

The Western Schism involved two rival popes, one in Rome, the other in Avignon. This lasted for nearly forty years beginning in 1378. Each pope declared the other one illegitimate. This was a confusing time for Catholics as no one was sure which pope to follow. The main effect of this schism was that it weakened people's confidence and faith in the Catholic Church and led to calls for reform. Over the next couple of hundred years, many reformers called into question the practices of Catholic leadership. This eventually led to the Reformation movement in which numerous new churches sprung up in protest of Catholic practices.

The Great Schism refers to the separation of the Catholic Church into the Roman Catholic Church and the Eastern Orthodox Church. The schism occurred mainly due to differences in beliefs about the authority of the pope, theological interpretations, and doctrinal differences. While the Great Schism was the formal separation that occurred in the year 1054 AD, the tensions and major disagreements that led to this schism have been ongoing for centuries.

At the time of the Great Schism, the Western churches (separated into the Roman Catholic Church) were led by Pope Leo IX, and the Eastern churches (separated into the Eastern Orthodox Church) were led by the patriarch of Constantinople, Michael Cerularius. The effects of the Great Schism are still present today through the cultural, religious, and language differences between those who practice in the Roman Catholic Churches and those who practice in the Eastern Orthodox Churches.

The "Great" or "Eastern" Schism refers to a break in the communion between the Roman Catholic and Orthodox Churches in 1054. This was actually part of a long process that began in the sixth century, continued through the Photian Schism, and really was not finalized until the Council of Florence in 1439, in which the two churches gradually drew apart over differences concerning spheres of influence, theology, language, and liturgy. 

The first major issue was the clash between the notion of papacy, in which the Bishop of Rome claimed to be the vicar of Christ on earth and have power over all other bishops as a "Pope," versus the eastern concepts of the "pentarchy" in which each bishop is responsible for his own diocese but the five patriarchs, bishops of the major cities of Rome, Jerusalem, Antioch, Constantinople, and Rome, are "primus inter pares."

Next, the Council of Toledo (in Spain) in 589 added the phrase "filioque" into the Nicene Creed. The Pope gradually approved a shift in the Roman liturgy to accept this phrase. The Eastern Church refused to accept that a local council and the Bishop of Rome (which they consider the proper title of the official the western church calls the Pope) had the right to unilaterally change a creed agreed upon by an ecumenical (universal) council. This led to a fundamental difference in which the Eastern Church argued that only ecumenical councils of the entire church can set forth authoritative statements about doctrine, while the western church argued that the Pope alone could do so. 

One major effect that the schism had was that in response to it the Roman Catholic Church attempted to articulate and clarify many of its own doctrines. Secondly, the ambivalent relationship between the churches led to the Crusades having two opposed motives of saving and conquering Constantinople. 

When we speak of the Great Schism, we can actually be referring to one of two schisms. The first is also called the East-West Schism and happened in 1054 when the Byzantine Church broke from the Roman Catholic Church. The second is also referred to as the Great Western Schism and happened between 1378 and 1417 when a pope in Rome and a second pope in Avignon, France, proclaimed themselves to be the real pope. Both schisms significantly affected the Roman Catholic Church. Though, typically, that which is called the Great Schism refers to the East-West Schism.

The greatest effect of the East-West Schism was the creation of two separate churches that had previously been unified under one church, the Eastern Orthodox Church and the Roman Catholic Church. But more specifically, the schism had developed over time due to "doctrinal, theological, linguistic, political, and geographic" differences; therefore, the schism also affected Catholicism by solidifying these differences (New World Encyclopedia, "Great Schism").

The greatest theological and political difference concerns the belief in the authority of the pope. The Roman Catholic Church holds that, as the successor of Saint Peter, the pope holds all authority over the Church. However, the Eastern Church feels the title of pope to be only an honorary one, so the church believes the pope has no authority to "determine policy" for all jurisdictions in the empire ("Great Schism").