How does the relationship between government and religion in zanj differ from the same relationship in dar al islam?

Zanj was a name used by medieval Muslim geographers to refer to both a certain portion of Southeast Africa (primarily the Swahili Coast), and to the area's Bantu inhabitants. The notions of "houses" or "divisions" of the world in Islam such as Dar al-Islam and Dar al-Harb does not appear in the Quran or the Hadith, the only authoritative sources of Islam.