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Up until AD 1054, beliefs in Orthodox Christianity remained relatively consistent despite recognized turbulence that spanned over centuries. The differences in political, cultural and theological background between Eastern and Western influences had been troublesome, evident in many less significant schisms between East and West, such as the schisms under Pope Damascus I, the Acacian schism between AD 482 and 519, and the Photian schism of AD 866 to 879, all of which were said to contribute to the strain that led to the Great Schism.
Throughout the history of the Roman empire, power shifts within the church were prominent and frequent. Many locales were regarded by many different people as centers of Christianity with insistence that the apostles had constructed several churches in the East, Rome the special exception of the West. This alone led to strain as to who might hold papal primacy among the authorities of the aforementioned churches. This struggle for power lasted centuries and was known to pervade Ecumenical Councils in regard to orthodox belief as well as trigger periods of separation between East and West before differences would eventually be reconciled.
What is normally regarded as the greatest tipping point is the mutual excommunication of 1054, whereupon Pope Leo IX demanded of Patriarch Cerularius of Constantinople to set aside his title as Ecumenical Patriarch and recognize Rome as the highest authority within Christianity. This came as a response to Cerularius closing churches in the East that supported Latin practices, an act that came in response to Greek churches being closed in southern Italy. When Cerularius refused the Pope’s demand, he was excommunicated by Cardinal Humbert. Cerularius, in turn, excommunicated the Cardinal.
It is unclear whether Cardinal Humbert even had the authority to excommunicate Cerularius, as Pope Leo IX had since died in office, and Cerularius’ actions were nothing more than a personal attack on the legate sent by the now-deceased Pope. However, it was exceedingly clear that the church had been separated distinctly by many different factors, not the least of which included ideology and geography. And while these particular events do not seem particularly significant, it was the beginning of progressively more and more aggressive action that refused to allow any reconciliation to take place.
After the Schism of 1054, many events occurred with the East and West interchangeably acting as the aggressor. The Crusades that involved military conflicts of European forces in Byzantine territory. The event known as the Massacre of the Latins in 1182. The Sacking of Thessalonica. The Siege of Constantinople. While religiously motivated, many (if not all) of these events and more superseded religious methods, resorting to shows of military strength that furthered the rift between Eastern and Western ideology as the course of history continued.
In 1965, a show of good faith was brought forth between Pope Paul VI and Patriarch Athenagoras I of Constantinople nullified the anathemas of 1054. Although this was little more than ceremonial in its efforts and signified no reunion between East and West, it has since brought forth religious leaders from both sides to convene annually in celebration of each other. Some Patriarchal leaders of recent memory have even attempted to strike a formal reunion between the Catholic and Orthodox churches, although this has been met with scrutiny and criticism from members of the Orthodox congregation.