The institution of the Khalifate had hardly been agreed upon when the question of who should occupy it became the subject of violent dissension. The first four khalîfs, whose reigns occupied the first thirty years after Mohammed's death, were Qoraishites, tribesmen of the Prophet, and moreover men who had been his intimate friends. The sacred tradition relates a saying of Mohammed: "The imâms are from Qoraish," intended to confine the Khalifate to men from that tribe. History, however, shows that this edict was forged to give the stamp of legality to the results of a long political struggle. For at Mohammed's death the Medinese began fiercely contesting the claims of the Qoraishites; and during the reign of Alî, the fourth Khalîf, the Khârijites rebelled, demanding, as democratic rigorists, the free election of khalîfs without restriction to the tribe of Qoraish or to any other descent. Their standard of requirements contained only religious and moral qualities; and they claimed for the community the continual control of the chosen leader's behaviour and the right of deposing him as soon as they found him failing in the fulfilment of his duties. Their anarchistic revolutions, which during more than a century occasionally gave much trouble to the Khalifate, caused Islâm to accentuate the aristocratic character of its monarchy. They were overcome and reduced to a sect, the survivors of which still exist in South-Eastern Arabia, in Zanzibar, and in Northern Africa; however, the actual life of these communities resembles that of their spiritual forefathers to a very remote degree.
Another democratic doctrine, still more radical than that of the Khârijites, makes even non-Arabs eligible for the Khalifate. It must have had a considerable number of adherents, for the tradition which makes the Prophet responsible for it is to be found in the canonic collections. Later generations, however, rendered it harmless by exegesis; they maintained that in this text "commander" meant only subordinate chiefs, and not "the Commander of the Faithful." It became a dogma in the orthodox Mohammedan world, respected up to the sixteenth century, that only members of the tribe of Qoraish could take the place of the Messenger of God.
The chance of success was greater for the legitimists than for the democratic party. The former wished to make the Khalifate the privilege of Alî, the cousin and son-in-law of the Prophet, and his descendants. At first the community did not take much notice of that "House of Mohammed"; and it did not occur to any one to give them a special part in the direction of affairs. Alî and Fâtima themselves asked to be placed in possession only of certain goods which had belonged to Mohammed, but which the first khalîfs would not allow to be regarded as his personal property; they maintained that the Prophet had had the disposal of them not as owner, but as head of the state. This narrow greed and absence of political insight seemed to be hereditary in the descendants of Ali and Fâtima; for there was no lack of superstitious reverence for them in later times, and if one of them had possessed something of the political talent of the best Omayyads and Abbasids he would certainly have been able to supplant them.
After the third Khalîf, Othmân, had been murdered by his political opponents, Ali became his successor; but he was more remote than any of his predecessors from enjoying general sympathy. At that time the Shî'ah, the "Party" of the House of the Prophet, gradually arose, which maintained that Ali should have been the first Khalîf, and that his descendants should succeed him. The veneration felt for those descendants increased in the same proportion as that for the Prophet himself; and moreover, there were at all times malcontents, whose advantage would be in joining any revolution against the existing government. Yet the Alids never succeeded in accomplishing anything against the dynasties of the Omayyads, the Abbasids, and the Ottomans, except in a few cases of transitory importance only.
The Fatimite dynasty, of rather doubtful descent, which ruled a part of Northern Africa and Egypt in the tenth century A.D., was completely suppressed after some two and a half centuries. The Sherîfs who have ruled Morocco for more than 950 years were not chiefs of a party that considered the legality of their leadership a dogma; they owe their local Khalifate far more to the out-of-the-way position of their country which prevented Abbasids and Turks from meddling with their affairs. Otherwise, they would have been obliged at any rate to acknowledge the sovereignty of the Great Lord of Constantinople. This was the case with the Sherîfs of Mecca, who ever since the twelfth century have regarded the sacred territory as their domain. Their principality arose out of the general political disturbance and the division of the Mohammedan empire into a number of kingdoms, whose mutual strife prevented them from undertaking military operations in the desert. These Sherîfs raised no claim to the Khalifate; and the Shî'itic tendencies they displayed in the Middle Ages had no political significance, although they had intimate relations with the Zaidites of Southern Arabia. As first Egypt and afterwards Turkey made their protectorate over the holy cities more effective, the princes of Mecca became orthodox.
The Zaidites, who settled in Yemen from the ninth century on, are really Shî'ites, although of the most moderate kind. Without striving after expansion outside Arabia, they firmly refuse to give up their own Khalifate and to acknowledge the sovereignty of any non-Alid ruler; the efforts of the Turks to subdue them or to make a compromise with them have had no lasting results. This is the principal obstacle against their being included in the orthodox community, although their admission is defended, even under present circumstances, by many non-political Moslim scholars. The Zaidites are the remnant of the original Arabian Shî'ah, which for centuries has counted adherents in all parts of the Moslim world, and some of whose tenets have penetrated Mohammedan orthodoxy. The almost general veneration of the sayyids and sherîfs, as the descendants of Mohammed are entitled, is due to this influence.
The Shî'ah outside Arabia, whose adherents used to be persecuted by the official authorities, not without good cause, became the receptacle of all the revolutionary and heterodox ideas maintained by the converted peoples. Alongside of the visible political history of Islâm of the first centuries, these circles built up their evolution of the unseen community, the only true one, guided by the Holy Family, and the reality was to them a continuous denial of the postulates of religion. Their first imâm or successor of the Prophet was Alî, whose divine right had been unjustly denied by the three usurpers, Abu Bakr, Omar, and Othmân, and who had exercised actual authority for a few years in constant strife with Khârijites and Omayyads. The efforts of his legitimate successors to assert their authority were constantly drowned in blood; until, at last, there were no more candidates for the dangerous office. This prosaic fact was converted by the adherents of the House of Mohammed into the romance, that the last imâm of a line of seven according to some, and twelve according to others, had disappeared in a mysterious way, to return at the end of days as Mahdî, the Guided One, who should restore the political order which had been disturbed ever since Mohammed's death. Until his reappearance there is nothing left for the community to do but to await his advent, under the guidance of their secular rulers (e.g., the shâhs of Persia) and enlightened by their authoritative scholars (mujtahids), who explain faith and law to them from the tradition of the Sacred Family. The great majority of Mohammedans, as they do not accept this legitimist theory, are counted by the Shî'ah outside Arabia as unclean heretics, if not as unbelievers.
At the beginning of the fifteenth century this Shî'ah found its political centre in Persia, and opposed itself fanatically to the Sultan of Turkey, who at about the same time came to stand at the head of orthodox Islâm. All differences of doctrine were now sharpened and embittered by political passion, and the efforts of single enlightened princes or scholars to induce the various peoples to extend to each other, across the political barriers, the hand of brotherhood in the principles of faith, all failed. It is only in the last few years that the general political distress of Islâm has inclined the estranged relatives towards reconciliation.
Besides the veneration of the Alids, orthodox Islâm has adopted another Shîitic element, the expectation of the Mahdî, which we have just mentioned. Most Sunnites expect that at the end of the world there will come from the House of Mohammed a successor to him, guided by Allah, who will maintain the revealed law as faithfully as the first four khalîfs did according to the idealized history, and who will succeed with God's help in making Islâm victorious over the whole world. That the chiliastic kingdom of the Mahdî must in the end be destroyed by Anti-Christ, in order that Jesus may be able once more to re-establish the holy order before the Resurrection, was a necessary consequence of the amalgamation of the political expectations formed under Shî'itic influence, with eschatological conceptions formerly borrowed by Islâm from Christianity.
The orthodox Mahdî differs from that of the Shî'ah in many ways. He is not an imâm returning after centuries of disappearance, but a descendant of Mohammed, coming into the world in the ordinary way to fulfill the ideal of the Khalifate. He does not re-establish the legitimate line of successors of the Prophet; but he renews the glorious tradition of the Khalifate, which after the first thirty years was dragged into the general deterioration, common to all human things. The prophecies concerning his appearance are sometimes of an equally supernatural kind as those of the Shîites, so that the period of his coming has passed more and more from the political sphere to which it originally belonged, into that of eschatology. Yet, naturally, it is easier for a popular leader to make himself regarded as the orthodox Mahdî than to play the part of the returned imâm. Mohammedan rulers have had more trouble than they cared for with candidates for the dignity of the Mahdî; and it is not surprising that in official Turkish circles there is a tendency to simplify the Messianic expectation by giving the fullest weight to this traditional saying of Mohammed "There is no mahdî but Jesus," seeing that Jesus must come from the clouds, whereas other mahdîs may arise from human society.