The First Council of Ephesus in 431 and the Council of Chalcedon in 451 condemned Nestorius and his doctrine, which emphasized the radical distinctness between Christ’s human and divine natures.
That forced a breach between the churches that defended Nestorius and the state church of the Roman Empire, which caused the Church of the East, the Christian church of Sassanid Persia, to become known as the Nestorian Church, as it took the side of Nestorius.
A large number of Nestorian Christians were expelled from Europe as heretics and came to Central Asia and the East. There was a community of Nestorian Christians in Ispidzhab (today’s Sayram) when Islam first came to Ispidzhab in 766 AD who resisted conversion from the detachment of Arabic and Arabic-speaking soldier-missionaries. Buddhism was also prevalent in Central Asia at that time.