The Great Schism

The Great Schism was the first major division within Christianity, it occurred in the 11^th century and separated the Church into Western (Roman Catholic) and Eastern (Orthodox) or Latin and Greek. It was the result of many years of disagreement over matters with Christian beliefs established by Ecumenical Councils. Cultural differences also played a role in this division of Christendom. 

The tipping point is believed to be the results of the Fourth Crusade. In 1204, Christian soldiers sent from Rome were destined for Egypt. The Crusaders lacked funds and provisions and were, out of necessity, enlisted to bring order to a Christian city. Pope Innocent, who initiated the Crusade, was angered by this and excommunicated the crusaders. This caused the crusaders to go to Constantinople, and they sacked the city and drove the Byzantines, the Eastern greek-speaking continuation of Roman Empire, into exile. There were efforts made to reunite the two churches, but in 1453 the Ottoman Empire conquered Constantinople and renamed it Istanbul and any hopes of a resolution were gone. Christianity was now divided into an Easter and Western Church.