Roman Catholic Church and the Greek Orthodox Church.
The tension between the western, Latin-speaking half of the church and the eastern, Greek-speaking half of the church built up over centuries of time. They argued over some doctrinal matters, such as whether the Holy Spirit proceeds from the Father and the Son (the West's confession) or from the Father alone (which was the East's insistence). But mainly the East-West struggle was about authority in the church. As the office of the Bishop of Rome sought to claim more universal authority for itself as the Papacy, the Patriarchs (church fathers) who governed in Constantinople objected. In 1054, the Western pope and the Eastern patriarch each excommunicated each other and the Western Schism had begun.
