Short answers, pulled from the story.
The word Divan originates from ancient Sumerian clay tablets bearing the root dub, which evolved through Old Persian and Elamite to Akkadian. The term traveled via Middle Persian dpyw' n and dyw' n before reaching English in 1586 as Oriental council of a state.
Caliph Umar created the first dīwān in 15 A.H. or more likely 20 A.H., which equals 636 CE or 641 CE. This initial army register contained names of warriors from Medina who participated in Muslim conquests alongside their families.
Three great departments headed the Buyid bureaucracy: finances, state chancery, and army. Military regime composed Turkish Daylamite troops made the army department particularly important with two armies existing turn eleventh century one Turks one Daylamites hence called department two armies.
Al-Mughira ibn Shu'ba established Basra's dīwān during his governorship between 636 and 638. Other garrison centers followed its organization including Kufa and Fustat.
Administrative authority in Tripoli was vested in a Pasha directly appointed by Sultan Constantinople after 1565. The Sublime Porte served as council ministers consisting Grand Vizier presiding other viziers kadi'askers nisanci defterdars.