The Church of Antioch is one of the five patriarchates (i.e., the Pentarchy) that constituted the one, holy, catholic, and apostolic Church before the schism between Rome and Antioch in 1098 and between Rome and the other patriarchates at around the same general period.
The early history of the Church of Antioch is detailed in the Acts of the Apostles, where in Acts 11:26 the Apostle Luke records that it was in that city that the disciples of Christ were first called Christians.
The remainder of the Church of Antioch, primarily local Greeks or Hellenized sections of the indigenous population, remained in communion with Rome, Constantinople, Alexandria, and Jerusalem.
Since the evangelists who preached the Gospel in Antioch came from Jerusalem where worship was in Syriac, it would only be natural that Syriac be the Liturgical language of the church of Antioch, and that she uses the Syriac liturgy of St. James the brother of the Lord and first bishop of Jerusalem.
The church of Antioch, therefore, is proud that her Liturgy is in Syriac, the language made holy by the Lord's divine tongue, and honored by the tongue of His mother Mary and his Apostles.
They split from the Syrian church of Antioch and established themselves a center of leadership in Madaen, Iraq, and then moved it, later on, to Baghdad in 762 A.D. Until recently, their church was known by the name "the Syrian church of the East", or the "Syrian Nestorian Church".