CAIRO - By declaring the establishment of an Islamic caliphate, the extremist group that controls large swaths of Syria and Iraq is claiming to be the successor of the political and religious community established by the Prophet Muhammad.
The caliphate is a powerful ideal -- the concept of a nation of Muslims worldwide ruled by Shariah law under a caliph who holds both spiritual and secular authority. There have been multiple caliphates over Islam's 1,400-year history, with the greatest Muslim empires ruling from Morocco to Central Asia.
The caliphate as an institution lost its authority centuries ago, becoming just a tool of secular rulers to give themselves religious backing. It was formally abolished in 1920 by Turkey's secular founder Mustafa Kamal Ataturk. And while many Muslims long for the unified community of the prophet's era, only a radical fringe are likely to see the Islamic State of Iraq and the Levant as its heir.
Here is a look at the history of the caliphate.
THE RIGHTLY GUIDED CALIPHS: The term caliphate comes from the Arabic word meaning succession, and the caliph is the title of those who assume the mantle of Muhammad as Muslims' spiritual and political leader. The first four leaders of the community who followed Muhammad in the 7th century are considered the purest expression of the caliphate -- Abu Bakr, Omar, Othman and Ali.
Chosen by "shura" -- or consultation among Muslims -- they led the community in its dramatic expansion from the Arabian Peninsula to rule over North Africa and the Middle East.
But the succession also carried the seeds of dispute. Shiites believe Ali should have directly succeeded Muhammad and leadership should have stayed in his line of the family. The wars that resulted -- eventually leading to Ali's death in 661-- solidified the Sunni-Shiite split that is now being violently played out in parts of the Mideast.
UMAYYADS AND ABBASIDS: After Ali's death, the caliphate moved to the Umayyad dynasty ruling from Damascus, which turnedd the caliph into a hereditary position. The dynasty ruled for nearly 100 years until it was defeated by the Abbasids, who claimed descent from an uncle of Muhammad.
The Abbasid caliphs, ruling from Baghdad, presided over Islam's golden age, patronizing scientists, Islamic scholars, philosophers and poets -- some of whom celebrated drinking, romance and other courtly pursuits in verses that would be brutally punished by today's ultraconservative Islamic State. But as the dynasty declined, often the caliph was reduced to a religious figurehead as other warring clans grabbed secular power.
Finally, the Mongols sacked Baghdad in 1258, ending the Abbasid dynasty. They are said to have killed the caliph at the time, al-Mustasim, by rolling him up in a carpet and trampling him with their horses.
It was a shattering blow to the already dwindling claim of a universal caliphate leading all Muslims. His heirs fled to Cairo, and while they kept the title of caliph, they were reduced to pawns of Egypt's Mamluk rulers.
OTTOMANS: As the Ottoman Empire became the pre-eminent Islamic power in the 15th and 16th centuries, its sultans claimed leadership of the entire Muslim world, eventually taking on the title of caliph, which was enshrined in the constitution in 1876. However, many Sunni scholars disputed their claim, arguing that the caliph must come from Muhammad's Arab tribe.
The Ottoman Empire was dismembered after World War I. Ataturk abolished the caliphate in 1924, removing the last caliph Abdulmecid II.
MODERN DREAMS: Nearly all Sunni political Islamist movements dream of the eventual resurrection of the caliphate, most by political means, though jihadi groups call for establishing it by violence. It has been the ultimate ambition of al-Qaida, but while its late leader Osama bin Laden could once claim leadership of the international jihadi movement, he never went so far as to declare himself caliph.
The Islamic State is hoping to rally extremists to its side. But even the militant camp is divided. Al-Qaida ejected the Islamic State from its network. Islamic militants in Syria have been battling the Islamic State since January, accusing it of hijacking the uprising against President Bashar Assad for its own transnational purposes.