The Schism of 1054 was a significant event in the history of Christianity which resulted in the formal division of the Western and Eastern Churches. The division was largely driven by theological, liturgical, and political differences between the Western Latin Church, centered in Rome, and the Eastern Orthodox Church, centered in Constantinople.
One of the key theological differences between the two Churches was the issue of the Pope's authority. The Western Church believed that the Pope held supreme authority over all the Churches, while the Eastern Church believed that all the five patriarchal sees (Rome, Constantinople, Alexandria, Antioch, and Jerusalem) were equal in authority and had jurisdiction over their respective territories.
Additionally, the use of a different version of the Nicene Creed in the liturgy, which was introduced by the Western Church, further contributed to the division. The Western Church added the filioque clause to the Nicene Creed, which stated that the Holy Spirit proceeds from the Father and the Son, whereas the Eastern Church held that the Holy Spirit proceeded only from the Father.
The political tensions between the Western and Eastern Roman Empires further exacerbated the situation, as the Eastern Church felt threatened by the growing power of the Western Church and the increasing encroachment of the Moors and the rise of Islam. The final straw was the mutual excommunication of the Pope and the Patriarch of Constantinople in 1054, which marked the formal split of the two Churches and is considered the official start of the Schism of 1054.