After the death of Prophet, there was a single Caliphate between AD 632 and AD 909 under different Caliphs (one after another) in Madina, Kufa, Damascus and Baghdad. During the intervening from AD 910 to 1516, there were more than one Caliphate at a time with head quarters located in different places like Baghdad, Tunisia, Cordoba, Almohad, Cairo and Istanbul. More than 600 years later again a single Caliphate under Ottoman Empire was established and lasted from AD 1517 to AD 1924. Mustafa Kemal Ataturk, the first ruler of modern Turkey, abolished Caliphate in 1924.
Caliphate of Islam has not evolved over the centuries like Papacy of Vatican. Position and duties of Pope gradually changed from an aggressively authoritative religious (and sometime political) leader of Catholics to their benign spiritual head now. Pope, however, never enjoyed the status of a Caliph i.e. the temporal and spiritual leader of faithfuls.
The issue of Caliphate has again come to picture about a decade back. Caliphate has been engraved in Muslim psyche as a glorious past. It represents an ideal aspiration for many Muslims. Unfortunately the concept of a future Caliphate has been used by both US and Islamic terrorists for their own interest. The US raises the bogey of Caliphate to continue its virtual hegemony in Middle East. Whereas, the Islamic terrorist groups are promoting the idea of a future Caliphate to get an uninterrupted supply of their killer volunteers.
The worn out Byzantine and Persian empires had helped in early and relatively easy Islamic expansion during seventh century consolidating the idea and practice of Caliphate. Presently we live in a totally different world. The Caliphate, as many Muslims may perceive, simply cannot return. The divergent interests of different Muslim and non-Muslim countries and people will disallow this to happen. The recent killing of Shi’a Muslims by minority but powerful Sunni Muslims in Iraq is a pointer. However, a benign Caliphate for spiritual purpose only can be thought of. But that is again doubtful as thousands of present day Islamic spiritual leaders in different Islamic countries will then loose the pre-eminence they enjoy now.