This text explores the history of the Eastern Church, spreading from Byzantium to the Orthodox Churches of the Balkans and Russia. It also examines the native Eastern Churches of Egypt, Ethiopia, Syria, Armenia and Georgia, and in the process exposes the many factors which contributed to the Christian disunity in the Middle Ages. The book also treats the impact on the East of such movements as the revolutionary Reform Papacy, the crusades, scolasticism and concilarism.