From the book Minorities in the Arab World , A.H. Hourani. Oxford University Press, 1947. 

The book is a  survey that covers ethnic, linguistic and religious minorities in Egypt, Palestine, Lebanon, Syria and Iraq.

These countries formed part of the Ottoman Empire for many centuries and the majority of their populations is Arabic in language and therefore to a great extent in culture. If they are taken as a whole, the majority of their population is Sunni Muslim.  

(1) The Orthodox Sunni Muslims are those who regard the Qur'an and the Traditions of the Prophet as the sole and sufficient repository of the Muslim faith. They do not recognize a need for a priesthood to mediate the faith to believers, or for an infallible interpretation of the holy writings. 

 Historically they sprang from the struggle for the succession to Muhammad. They regards the headship of the Islamic community as having passed form the Prophet to the Orthodox Caliphs: Abu Bakr, Umar, Uthman and Ali, and then to the Umayyads. They look on the Caliphs as the temporal rulers only, with no supernatural power or excellence. 

(2) The Shi'is.

 The split between Sunnis and Shi'is began in the first century of Islam, with the struggle for the Caliphate between Ali ibn Abu Talib, the Prophet's son-in-law, and Muawiya ibn Abu Sufian. The partisans of Ali, the Shi'a, clung to his cause even after his death in AD 661 and that of his son Hussein in AD 680. Moulded into a compact unit by the persecutions to which Umayyads and Abbasids alike subjected them, they have preserved throughout the centuries the distinctive features  which differentiate them form the orthodox Sunnis. 

Their most obvious characteristic is the cult of the Prophet's family in general and particularly of Ali, or rather the legendary figure which has been constructed around the historical Ali. They believe that the Imamate, the combined secular and spiritual leadership of Islam, passed form the Prophet to Ali, in whose family it them inhered. The Imam is the interpreter of the law and doctrine, and as such infallible and impeccable, and loyalty to him is regarded as the sixth pillar of Islam.  

The majority of Shi'is believe that the line of Imams died out with the twelfth who disappeared during the ninth century AD and has since been “hidden”, until such time as he shall reappear to rule the world and give his faithful adherents their due. The Zaidis of Yemen recognize three of these Imams only, and the Isma'ilis six. 

(3)  The Alawis. 

They are also known as Nusairis and have a religion which possesses many of the characteristics of dissident Islam, but may non-Islamic elements as well. Like the Druze, their religion originated  through the desire of the indigenous inhabitants of Syrian hill country to preserve their solidarity and distinctiveness, while at the same time outwardly conforming to the beliefs of the rulers of the country. 

From Paganism (either directly or by way of the Isma'ilis) the Alwais took over the idea of a Divine Triad, of its successive incarnations in the seven cycles of world history, and of the transmigration of souls. From Shi'a Islam they adopted and exaggerated the cult of Ali, whom they regard as they incarnation of the Divinity, and form Isma'ilism the idea of an esoteric teaching hidden form the masses and revealed only to the initiates after a complex process of initiation. From Christianity they appear to have derived much of the ritual, the possession of which distinguishes them from other Islamic sects. 

(4) Isma'ilis.

They split off form the Shi'is in the eighth century over the question of the succession to the Imamate. They maintain that the genuine line was continued through Isma'il, the eldest son of the sixth Imam, while the Shi'is recognize Isma'il's brother Musa and his descendants. 

The Isma'ilis carried further two tendencies inherent in Shi'ism: first they insisted on the necessity of an esoteric teaching placed above human discussion and dispensed to a chosen body of initiates by the Imam. They developed a body of philosophical doctrines which took them very far from Islam:  doctrines of emanation, incarnation, revelation and transmigration. 

Secondly they insisted on the duty of blind obedience to the Imam. The habit of devotion thus formed among them was more than once used by ambitious individuals for their own aggrandizement or for purposes of political revolution.  

(5)  The Druze.

The religion of the Druze may be regarded as an offshoot of Isma'ilism. Historically it springs from the Fatimid Caliph of Egypt, Hakim (AD 996-1020) , who gave himself out to be the final incarnation of the deity. His followers Hamza and Darazi spread his doctrine among the inhabitants of southern lebanon, and founded among them a sect whom the outside world called “Druze”, and they called themselves “Unitarians” . They believe that Hakim, the last incarnation of god, is not dead but will return. They also believe in emanations of the deity, in supernatural hierarchies and transmigration of the soul. They practice systematic concealment of their beliefs, which are not know fully even to all members of the faith, but only to the initiates among them.