Eastern Christianity

=== Church of the East ===
{{Main|Church of the East|Nestorianism|Lakhmids}}
Historically, the Church of the East was the widest reaching branch of Eastern Christianity, at its height spreading from its heartland in [[Persia]]n-ruled [[Assyria]] to the Mediterranean, India, and China. Originally the only Christian church recognized by [[Zoroastrian]]-led [[Sassanid Empire|Sassanid Persia]] (through its alliance with the Lakhmids, the regional rivals to the Byzantines and its [[Ghassanid]] vassal), the Church of the East declared itself independent of other churches in 424 and over the next century became affiliated with Nestorianism, a Christological doctrine advanced by [[Nestorius]], [[Ecumenical Patriarch of Constantinople|Patriarch of Constantinople]] from 428 to 431, which had been declared heretical in the Roman Empire. Thereafter it was often known, possibly inaccurately, as the Nestorian Church in the West. Surviving a period of persecution within Persia, the Church of the East flourished under the [[Abbasid Caliphate]] and branched out, establishing dioceses throughout Asia. After another period of expansion under the [[Mongol Empire]], the church went into decline starting in the 14th century, and was eventually largely confined to its founding [[Assyrian people|Assyrian]] adherent's heartland in the [[Assyrian homeland]], although another remnant survived on the [[Malabar Coast]] of India.

In the 16th century, dynastic struggles sent the church into schism, resulting in the formation of two rival churches: The [[Chaldean Catholic Church]], which entered into communion with Rome as an Eastern Catholic Church, and the Assyrian Church of the East. The followers of these two churches are almost exclusively ethnic Assyrians. In India, the local Church of the East community, known as the Saint Thomas Christians, experienced its own rifts as a result of Portuguese influence.

==== Assyrian Church of the East ====
{{Main|Church of the East|Assyrian Church of the East}}
The Assyrian Church of the East emerged from the historical Church of the East, which was centered in Mesopotamia/Assyria, then part of the [[Sasanian Empire|Persian Empire]], and spread widely throughout Asia. The modern Assyrian Church of the East emerged in the 16th century following a split with the Chaldean Church, which later entered into communion with Rome as an Eastern Catholic Church.

The Church of the East was associated with the doctrine of Nestorianism, advanced by Nestorius, Patriarch of Constantinople from 428 to 431, which emphasized the disunion between the human and divine natures of [[Jesus]]. Nestorius and his doctrine were condemned at the Council of Ephesus in 431, leading to the [[Nestorian Schism]] in which churches supporting Nestorius split from the rest of Christianity.

Many followers relocated to Persia and became affiliated with the local Christian community there. This community adopted an increasingly Nestorian theology and was thereafter often known as the Nestorian Church. As such, the Church of the East accepts only the first two ecumenical councils of the undivided Church—the First Council of Nicaea and the First Council of Constantinople—as defining its faith tradition, and rapidly took a different course from other Eastern Christians.

The Church of the East spread widely through Persia and into Asia, being introduced to India by the 6th century and to the Mongols and China in the 7th century. It experienced periodic expansion until the 14th century, when the church was nearly destroyed by the collapse of the Mongol Empire and the conquests of [[Timur]]. By the 16th century it was largely confined to Iraq, northeast Syria, southeast Turkey, northwest [[Iran]] and the Malabar Coast of India ([[Kerala]]). The split of the 15th century, which saw the emergence of separate Assyrian and Chaldean Churches, left only the former as an independent sect. Additional splits into the 20th century further affected the history of the Assyrian Church of the East.

==== Saint Thomas Syrian Christians ====
{{Main|Saint Thomas Christians}}
The [[Saint Thomas Christians|Saint Thomas Syrian Christians]] are an ancient body of [[Syriac Christianity|Syrian Christians]] in Kerala, Malabar coast of [[India]] who trace their origins to the evangelical activity of [[Thomas the Apostle]] in the 1st century. Many [[Assyrian people|Assyrian]] and [[Jews|Jewish]] communities like the [[Knanaya]] and the [[Cochin Jews]] assimilated into the [[Saint Thomas Christian|Saint Thomas Syrian Christian]] community.<ref name="AFM">A. E. Medlycott, ''India and The Apostle Thomas'', pp. 1-71, 213–297; M. R. James, ''Apocryphal New Testament'', pp. 364–436; Eusebius, ''History'', chapter 4:30; [[J. N. Farquhar]], ''The Apostle Thomas in North India'', chapter 4:30; V. A. Smith, ''Early History of India'', p. 235; L. W. Brown, ''The Indian Christians of St. Thomas'', pp. 49–59</ref> By the 5th century the Saint Thomas Syrian Christians were part of the [[Church of the East]] ([[Nestorian Church]]). Until the middle of the 17th century and the arrival of the [[Portuguese India|Portuguese]], the Thomas Christians were all one in faith and rite. Thereafter, divisions arose among them, and consequently they are today of several different rites. The [[East Syriac Rite|East Syriac Chaldean Rite]] (Edessan Rite) Churches among the Saint Thomas Syrian Christians are the [[Syro-Malabar Church|Syro Malabar Church]] and the [[Chaldean Syrian Church]]. The [[West Syriac Rite|West Syriac Antiochian Rite]] Churches among the Saint Thomas Syrian Christians are the [[Jacobite Syrian Christian Church|Malankara Jacobite Syrian Church]], the [[Malankara Orthodox Syrian Church]], the [[Mar Thoma Syrian Church]], the [[Syro-Malankara Catholic Church|Syro Malankara Church]] and the [[Malabar Independent Syrian Church|Thozhiyur Church]].