The Great Schism was a period of time in the 11th century when the Roman Catholic Church and the Eastern Orthodox Church split into two separate entities. This split had a major impact on the Byzantine Empire, as the Eastern Orthodox Church was the official religion of the empire. The Great Schism caused a rift between the Eastern and Western churches, and the Byzantine Empire was caught in the middle. This led to a decline in the power of the Byzantine Empire, as the two churches were no longer unified and the empire was no longer able to rely on the support of the Western Church. (Source: Holt McDougal World History: Patterns of Interaction, Chapter 10, Section 2)
