Catholicism and Orthodoxy c. 1000

In 1054 the lengthy process of the East–West Schism began after Pope Leo IX sent a legate to Constantinople to dispute the eastern interpretation of the Holy Trinity and to proclaim his right to be head of both the western and eastern Churches. When Michael I Cerularius, head of the church in Constantinople, rejected the Pope’s claims, the Pope’s representative excommunicated Cerularius. Cerularius then excommunicated Pope Leo IX, who had in fact recently died, and his representatives. This incident was the culmination of a lengthy separation of customs and power between the two churches, which traces its roots back to the separation of the Eastern and western Roman Empires. From this point the schism widened until the two Churches completely separated. As a result, two branches of Christianity were propagated in different regions and frequently clashed during periods of conquest, such as the Fourth Crusade in 1204 when Catholic forces sacked Constantinople.