In 1054, the leaders of the Eastern (Greek) and Western (Roman) Churches excommunicated each other, which became known as the Great Schism or East-West Schism. This meant that they officially cut off communion with each other and declared the other side as heretical. The main reason for this action was the increasing theological, cultural, and political differences between the two branches of Christianity. The Schism resulted in the permanent split between the Eastern Orthodox Church and the Roman Catholic Church, contributing to the division of Christianity into two major branches that persist to this day.
