Islam expands

Patriarchs of Jerusalem, Antioch, and Alexandria fall into non-Roman (imperial) boundaries and new Caliphs achieve political strength, sometimes helping the Orthodox and at other times abusing the Christian Orthodox. https://en.wikipedia.org/wiki/Christianity_in_pre-Islamic_Arabia# The Church of the East's center, Seleucia-Ctesiphon, shifted towards Mosul and the Nineveh Plain around the 7th-13th centuries, especially as Syriac Orthodox Christians fled persecution from cities like Tikrit (Tagrit) to Mosul, establishing churches like the Mar Ahûdêmmêh (Hûdéni) Church, making Mosul a significant regional hub before later moves due to conflict, like during World War I, to places like Chicago, then back to Iraq in 2015. Also see https://www.denver.goarch.org/influence-of-islam-on-orthodox-christianity