Complex sentence: The Turkmens reside in the north of the province, a plain called Turkmen Sahra, this former nomadic people live in this area from 15th century, main cities of whom is Gonbad-e Kavus and Bandar Torkaman.
Split into simpler sentences: The Turkmens reside in the north of the province, a plain called Turkmen Sahra. From the 15th century, these formerly nomadic people have lived in this area, the main cities of which are Gonbad-e Kavus and Bandar Torkaman.