(or Assyrian Church of the East),
often misleadingly called the Nestorian Church. The Church in Mesopotamia (roughly modern Iraq) was outside the Roman Empire and took no part in the great Councils, though the Creed and Canons of Nicaea (325), affirming the Divinity of Christ, were formally accepted in 410. The Council of Ephesus (431), and especially the title ‘Theotokos’ for the BVM, is rejected. Attitudes to the Definition of Chalcedon are ambivalent, because of a different understanding of the term hypostasis. The liturgical language is Syriac.
In the 4th–5th cents. the Church suffered intermittent persecution. A monastic revival in the 6th cent. led to a large number of new foundations and by the early 7th cent. missionaries from the Church of the East had reached China. By the end of Sassanian rule in Iran (651) Christians constituted an important religious minority in that country. The Church of the East suffered drastic losses in the 14th cent., after the conversion of the Mongol dynasty to Islam in 1295. In the mid-16th cent. it was divided by the creation of a separate Uniat line of Patriarchs (see Chaldean Christians). Several missions were sent from the West in the 19th cent. In the 20th cent. the Church of the East suffered as a result of political developments, and its members are now scattered over many parts of the world, especially the USA; only about 30,000 remain in the Middle East. Since 1968 there has been a schism, with one Catholicos resident in Baghdad, the other in the USA.