Complex sentence: From the ninth century Christians began to migrate northwards, many settled in Mosul and its environs especially Bakhdida as well as Tur Abdin mainly due to restrictive measures taken by some Muslim governors.
Split into simpler sentences: From the ninth century Christians began to migrate northwards. Many settled in Mosul and its environs, especially Bakhdida, as well as Tur Abdin mainly due to restrictive measures taken by some Muslim governors.