In the first century, the disciple Thaddeus brought Christianity to the Persian Empire, establishing what came to be known as the Church of the East. This kingdom-minded church took Christianity to China, India, Southeast Asia, Mongolia, and even Siberia. At one time, these Christians encompassed a geographical area greater in size than that of the Roman Catholic Church. However, when these Christians refused to give Mary the title, “Mother of God,” the Catholic Church branded them as heretics and labeled them as Nestorians.
In reality, Nestorius, the bishop of Constantinople, was never a member of this church. However, like the Church of the East, he felt that to give Mary the title of "Mother of God" or Theotokos, would lead to her being venerated—which, in fact, is the very thing that happened.