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[1] (see Constitution of Medina), meaning that the head of state (the Caliph) and other officials are dicate to the people according to Islamic law, which excercises power over their 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 was a personal matter. It was the world's first major welfare state.[2] (Although this is also claimed by the Mauryan Empire, 800 years earlier)[3]. 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.[4] 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."