The first enduring Christian divisions: From Ephesus and Chalcedon to the Second Council of Nicaea, AD 431-787

This chapter reconstructs the first enduring divisions of ancient Christianity from the Council of Ephesus in AD 431 to the Second Council of Nicaea in 787. It argues that the conventional focus on 1054 obscures older fractures produced by the interaction of Christological controversy, conciliar reception, linguistic translation, patriarchal rivalry, imperial policy, regional identity, and coercive enforcement. The chapter explains the dispute among Nestorius, Cyril of Alexandria, and their supporters over the unity of Christ and the title Theotokos; the rival proceedings at Ephesus; the formation and Asian expansion of the East Syriac Church of the East; the crisis from Eutyches and Ephesus 449 to Chalcedon's Definition of one Christ in two natures; and the gradual consolidation of Coptic, Syriac, Armenian, Ethiopian, and related non-Chalcedonian traditions now known as Oriental Orthodox. It then traces the Henotikon, the Acacian Schism, Justinian's reunion policies, Constantinople II, the monothelite controversy, Constantinople III, and the Byzantine icon controversy culminating at Nicaea II. Modern ecumenical agreements are used to distinguish historic polemical labels from present official Christological self-understanding. Genealogically, the period produced durable East Syriac, Chalcedonian, and Oriental Orthodox trajectories long before the East-West Schism. A Sola Scriptura assessment affirms the biblical necessity of confessing one Lord Jesus Christ as fully divine and fully human, while testing conciliar authority, imperial coercion, Marian terminology, and icon veneration by the apostolic Scriptures.

Keywords: Council of Ephesus; Council of Chalcedon; Church of the East; Oriental Orthodox; Christology; miaphysitism; iconoclasm; Second Council of Nicaea