order to issue valid legal rulings. In many ways, classical Islamic law functioned like a constitutional law. Practically, for hundreds of years after the fall of the Rāshidūn Caliphate (7th century CE) and until the first half of the 20th century, Muslim-majority countries usually adopted a system of government based on the coexistence of the sultan and ulama which followed the rules of the sharia law. This system resembled to some extent some Western governments in possessing an unwritten constitution (like the United Kingdom), and possessing separate, countervailing branches of government (like the United States), which provided a clear separation of powers in socio-political governance. While the United States and some other systems of government have three separate branches of government—executive, legislative, and judicial—Islamic monarchies had two: the sultan and the ulama. According to the French political scientist and professor Olivier Roy, this "de facto separation between political power" of sultans and emirs and religious power of the caliph was "created and institutionalized ... as early as the end of the first century of the hegira." The sovereign's religious function was to defend the Muslim community against its enemies, institute the sharia, ensure the public good (maslaha). The state was instrument to enable Muslims to live as good Muslims and Muslims were to obey the sultan if he did so. The legitimacy of the ruler was "symbolized by the right to coin money and to have the Friday prayer (Jumu'ah khutba) said in his name." British lawyer and journalist Sadakat Kadri argues that a large "degree of deference" was shown to the caliphate by the ulama and this was at least at times "counterproductive". "Although jurists had identified conditions from mental incapacity to blindness that could disqualify a caliph, none had ever dared delineate the powers of the caliphate as an institution." During the Abbasid caliphate: When Caliph Al-Mutawakkil had been killed in 861, jurists had retroactively validated his murder with a fatwa. Eight years later, they had testified to the lawful abdication of a successor, after he had been dragged from a toilet, beaten unconscious, and thrown into a vault to die. By the middle of the tenth century, judges were solemnly confirming that the onset of blindness had disqualified a caliph, without mentioning that they had just been assembled to witness the gouging of his eyes. According to Noah Feldman, law professor at Harvard University, the Muslim legal