The term caliphate (from the Arabic خلافة or khilāfa, Turkish: Halife ) refers to the first system of government established in Islam, and represented the political unity of the Muslim Ummah (nation). In theory, it is a constitutional republic, meaning that the head of state (the Caliph) and other officials are representatives of the people who must govern according to Islamic law; which limits the government's power over citizens. It was initially led by Muhammad's disciples as a continuation of the political system the prophet established, known as the 'rashidun caliphates'. It represented the political unity, not the theological unity of Muslims as theology or mazhab was a personal matter. It was the world's first major welfare state. A "caliphate" is also a state which implements such a governmental system. Sunni Islam dictates that the head of state, the caliph, should be selected by Shura – elected by Muslims or their representatives. Followers of Shia Islam believe the caliph should be an imam descended in a line from the Ahl al-Bayt. After the Rashidun period until 1924, caliphates, sometimes two at a single time, real and illusory, were ruled by dynasties. The first dynasty was the Umayyad. This was followed by the Abbasid, the Fatimid, and finally the Ottoman Dynasty. The caliphate was "the core political concept of Sunni Islam, by the consensus of the Muslim majority in the early centuries."