Answer:
The Great Schism occurred in 1054 when the patriarch of Constantinople (present-day Istanbul) broke with the pope in Rome and the Roman Catholic Church, partly because of the pope's association with the German emperor.
The Christian Church in Eastern Europe and the Middle East developed in various national directions, for example the Greek Orthodox Church, the Russian Orthodox Church, but with the Patriarch of Constantinople as the common head. The breach was also crucial to the witheredness of the connection between Western and Eastern Europe, which had been around since the collapse of the West Roman Empire in the 5th century.
The relationship between Rome and Constantinople was emotionally damaged above all by the events of the Fourth Crusade, when Constantinople was conquered by the Venetians in 1204. Today, historians agree that the churches separated due to progressive alienation that coincided with the growth of the papal authority. Decisive for the separation were not theological differences, but church political factors.