Christianity was a major unifying factor between Eastern and Western Europe before the Arab conquests, but the conquest of North Africa sundered maritime connections between those areas. Increasingly the Byzantine Church differed in language, practices, and liturgy from the western Church. The eastern church used Greek instead of the western Latin. Theological and political differences emerged, and by the early and middle 8th century issues such as iconoclasm, clerical marriage, and state control of the church had widened to the extent that the cultural and religious differences were greater than the similarities. The formal break came in 1054, when the papacy and the patriarchy of Constantinople clashed over papal supremacy and excommunicated each other, which led to the division of Christianity into two churches—the western branch became the Roman Catholic Church and the eastern branch the Orthodox Church.
Over what issue did the eastern and western churches split?
papal supremacy