"A caliphate (in Arabic: خلافة khilāfa, meaning "succession") is an Islamic state led by a supreme religious and political leader known as a caliph – i.e. "successor" – to Muhammad. The succession of Muslim empires that have existed in the Muslim world are usually described as "caliphates". Conceptually, a caliphate represents a sovereign polity (state) of the entire Muslim faithful (the Ummah, i.e. a sovereign nation state) ruled by a single caliph under the Constitution of Medina and Islamic law (sharia)."
Basically, one's status as a caliph is dependent on the acceptance of that status by some group of Muslims. This follows the general pattern of religio/political formation through consensual agreement.in Islamic and Arab culture. This applies in; ideas, law, government, etc.
The declaration of the caliphate of Abu Bakr al-Baghdadi (Caliph Ibrahim) is a declaration of war against each and every existing Arab and Muslim government because in the presence of a supposed caliph all their governments must be viewed as illegitimate usurpations of the caliph's divinely given religious and political authority.
The supposedly undivided and sole authority of a caliph has always been a difficulty in the Sunni Islamic World for development of what we would see in the West as secular government. In the Enlightenment we in the West came to believe in the idea of a separation of church and state. That never happened in Islam. In Islamic history the authority of the caliph was always remembered, revered and claimed among Sunni Muslims as a basis for legitimacy. Saladin exercised power as sultan under the justifying endorsement of an Abbasid caliph in Baghdad. The khedive of Egypt's rule was legitimized by recognition of the Ottoman sultan/caliph as his lord. The khedive's officers and soldiers wore Ottoman uniforms, were given Ottoman decorations , held their commissions in the sultan/caliph's name and the khedive's government flew the Ottoman flag.
In Shia lands the authority of the Ottoman sultan/caliph or any other dynasty of Sunni caliphs was ignored through the "simple' expedient of denying their authenticity as caliphs. i suppose it is theoretically possible for there to be a Shia caliph/imam in the person of the mahdi when he comes.
The destruction of the Ottoman Empire in WWI marked the end of the Ottoman Caliphate and the claimed umma wide authority of the caliph. Since that time governments in Sunni lands; Egypt, Jordan, Iraq, Pakistan, Indonesia, etc. have looked to internal sources of legitimacy whether they were; Alid descent, constitutional and representative governments or whatever. Some governments have claimed several bases but none have relied on the authority of a caliph. At the same time these states have accepted the borders dictated by the colonial powers and at Versailles.
Now ,we have the "caliphate" of abu bakr al-baghdadi (Ibrahim). this dream of Islamic empire claims the authority of the; Ummayads, Abbasids, Fatimids and Ottomans. It demands obeisance from all Muslims, eventual destruction of "dissident" Islamic communities, and the elimination of borders. It does not recognize the post Westphalia world system. For this reason we see videos of ISIS jihadis burning their passports.
IMO, this declaration of the caliphate of Ibrahim is a terrible blunder for ISIS. The Islamic world will unite in hostility against such ambitions and claims. Most people in these countries want to retain their local national ientities or at least to have states that may better reflect their ethnic identity. Even the Saudis, who have toyed with the notion of absulute authority given to their wahhabi faith, will recooil in horror from the evident threat presented by the idea of an umma ruled by the likes of these people.
In the immediate situation of Iraq, surely this declaration will accelerate th breakup of the Sunni Arab coalition. pl