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 (see Constitution of Medina), 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.
The caliph was often known as Amir al-Mu'minin (أمير المؤمنين) "Commander of the Believers". Muhammad established his capital in Medina, and after he died it remained the capital for the Rashidun period. At times in Muslim history there have been rival claimant caliphs in different parts of the Islamic world, and divisions between the Shi'a and Sunni communities.
According to Sunni Muslims, the first caliph to be called Amir al-Mu'minin was Abu Bakr Siddique, followed by Umar ibn al-Khattāb, the second of the Four Rightly Guided Caliphs. Uthman ibn Affan and Ali ibn Abi Talib also were called by the same title, while the Shi'a consider Ali to have been the first truly legitimate caliph, although they concede that Ali accepted his predecessors, because he eventually sanctioned Abu-Bakr.
The rulers preceding these first four did not receive this title by consensus, and as it was turned into a monarchy thereafter.
After the first four caliphs, the Caliphate was claimed by dynasties such as the Umayyads, the Abbasids, and the Ottomans, and for relatively short periods by other, competing dynasties in al-Andalus, North Africa, and Egypt. Mustafa Kemal Atatürk officially abolished the last Caliphate, the Ottoman Empire, and founded the Republic of Turkey, in 1924. The Kings of Morocco still label themselves with the title Amir al-Mu'minin for the Moroccans, but lay no claim to the Caliphate.
Some Muslim countries, like Indonesia and Malaysia were never subject to the authority of a Caliphate, with the exception of Aceh, which briefly acknowledged Ottoman suzerainty. Consequently these countries had their own, local, sultans or rulers who did not fully accept the authority of the Caliph