Eastern Christianity
Church of the East

Historically, the Church of the East was the widest reaching branch of Eastern Christianity, at its height spreading from its heartland in Persian -ruled Assyria to the Mediterranean, India, and China. Originally the only Christian church recognized by Zoroastrian -led 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, Patriarch of Constantinople from 428 to 431, which had been declared heretical in the Roman Empire. Thereafter it was often known in the West, possibly inaccurately, as the Nestorian Church. 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 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.
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