Eastern Christianity
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 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.
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