The Great Schism of 1054 marked the official split between the Eastern Orthodox Church of Constantinople and the Roman Catholic Church. The churches separated due to a mix of religious, cultural and political disagreements.

The Eastern Orthodox Church understood the importance of the Pope yet rejected Papal supremacy. They did not believe the Pope had universal jurisdiction over every Christian church. The Roman Catholic Church believed the Pope had Papal supremacy which implied he had the right to make decisions about Catholics around the world.

Forty one years after the Great Schism, in 1095, the emperor of the Byzantine Empire asked Pope Urban II to supply the Byzantine Empire with military aid to protect the Empire from the advances of the Seljuk Turks.

Pope Urban II passionately advocated for supplying military aid to the Byzantine Empire to protect them from the Seljuk Turks. He stated that the Easter Orthodox Byzantines were their Christian brethren and therefore were commanded by God to protect them from foreign invasions. The Byzantines were grateful to the Crusaders for their military aid.  

The Sack of Constantinople eliminated any opportunity for peace or interreligious relations in the near futureIt was not until the 1960 that the Catholic Church began the process of re-establishing relations with the Eastern Orthodox Church. However, the Eastern Orthodox Church was not open to re-establishing relations, untrusting of the Catholic Church.

 After repeated efforts from the Catholic Church to establish a connection, including inviting The Orthodox Church to the Second Vatican Council, Ecumenical Patriarch Bartholomew formally accepted the Catholic Church’s apology.