From A Concise History of Romania (Cambridge Concise Histories), by Keith Hitchins (Cambridge, 2014), Kindle Loc. 581-601:
The juridical relationship that evolved between the principalities and the Ottoman state in the fifteenth and sixteenth centuries owed as much to Ottoman pragmatism and legal theory as to the political and social conditions prevailing in Moldavia and Wallachia and the international circumstances of the time. From the perspective of the Islamic law of nations, which the Ottomans observed, the principalities lay in an intermediate zone between dar al-harb (the domain of war), that is, territories contested between the Muslim state and its enemies, and dar al-Islam (the domain of Islam), territories where their inhabitants were subject to a Muslim ruler and Islamic law. The principalities by the sixteenth century clearly no longer belonged to the former, but they had not entered the latter. Some historians have placed them in dar al-sulh (the domain of peace) or dar al-‘ahd, territory acquired by the Muslim ruler by treaty; still others, in accordance with the Hanafite school of law, which predominated in the Ottoman Empire, have assigned them to dar al-muvâda’a (the domain of armistice) or dar al-dhimma (the domain of protection and tribute). The latter two terms may represent most accurately the two main phases through which Ottoman–Romanian relations passed, the years 1538–41 marking the dividing line. At the beginning of their encounter, the principalities were vassal states obliged to pay the tribute and render military service, and, then, as the relationship grew tighter, the sultan, for his part, assumed certain responsibilities toward the principalities, notably to give them protection.
The arrangement that thus emerged enabled Moldavia and Wallachia to escape incorporation into the Ottoman political system, as had happened to the Christian states south of the Danube. Various ‘ahd-names and berāts (writs of appointment) granted by the sultans allowed the principalities almost full internal autonomy. Thus, the sultan acknowledged the right of the prince and the boiers to rule “in accordance with custom” and forbade Turkish civil and military officials or the Muslim clergy to involve themselves in the internal affairs of the principalities. He allowed the boiers to elect the prince, but reserved to himself the right to approve their choice and to invest the new prince with the insignia of his office. As a consequence of autonomy, the laws and legal system, the social structure, landholding and agrarian relations, cultural and intellectual life, and the status of the Orthodox Church were left unchanged. But the sultan took charge of foreign affairs, prohibiting the princes from maintaining diplomatic contacts with foreign states or conclude treaties with them, and he undertook to defend the principalities against foreign attack.