The two different branches in Islam are Sunni and Shia sects. There are also their sub-denominations or other orders such as Ahmadiyya, Alawi, Druze, Hanafi, Ismaili, Jafari, Kharijite, Maliki, Shafi, Sufi, Wahabi, Zaidi, etc. Just as within Christianity, there are different denominations in Islamic faith, but these two are the major ones practiced by 1,6 billion Muslims around the world.
Sunni's are the main group in Islam, making up 85-90% of the religion's adherents. Has been dominating almost continuously since 661, when the Shi'is departed from the main fold (the Kharijis left in 658). Sunni Islam claims to be the continuation of the Islam as it was defined through the revelations given to Muhammad and his life, a claim which is substantiated through the fact that Shi'i Islam for a number of decades had very little following and had no real, formal organization. As for the theology, Sunni Islam represents no more of a continuation of Islam than the other orientations.
Sunni Islam has its name from its identification with the importance of the Sunna (the examples from the hadiths), which earlier than in Shi'i Islam was established as central to the true image of Islam. This was connected to the need of establishing a law, called Shari'a - Seriat (for which the hadiths served as a central source), as Sunni Islam was the religious orientation of the rulers, while the Shi'is did not establish administrative organizations for a long time.
The actual theological and ritual differences between Sunni and Shi'i Islam, came over a couple of centuries with development. For a long time, Sunni Islam was defined from Shi'i Islam by its adherence to the Caliph as the leader of the Muslim world.
There are many smaller and some larger differences between Sunni and the two other orientations, in all aspects of the religion. Sunni and Shi'i Islam share only three core doctrines, oneness of God, the belief in the revelations of Muhammad, and the belief in resurrection on the Day of Judgment.
Sunni Islam has a different set of hadiths from Shi'i Islam. In Sunni Islam, there are performed 5 prayers a day, while Shi'i Islam has only 3. Sunni Islam puts far more importance into the hajj to Mecca, while Shi'i Islam has some other central pilgrimages as well. Sunni Islam revere Ali, but does not hold him up the only true continuation of the tradition from Muhammad, and has no emphasis on him bringing on a divine light from the Prophet. While Sunnis rely heavily on the practice of the Prophet and his teachings (the "Sunna"), the Shi'i see their Ayatollahs as reflections of God on Earth.
About 85% of the population in Turkey are Sunni.
The largest non Sunni branch of Islam, the Shi'i, in their various forms represent some 10-15% of the Muslim world. The term Shi'i refers to the partisans of the fourth Caliph Ali, who was Muhammad's son in law through his daughter Fatima, the last Caliph to be elected, as well as the last to be drawn from the original nucleus of converts from the Mecca - Medina period. The Shi'i, in their various forms, are significant minorities in Lebanon, Syria, Saudi Arabia, Yemen, Bahrain, the Gulf States, Pakistan and India. They represent the largest religious group in Iraq, and the overwhelming majority (88%) in Iran, where Shi'i Islam has been the state religion since the 16th century AD.
The seeds of schism were planted upon the deathbed of the Prophet Muhammad, when, according to Shi'i tradition, he indicated that Ali be his successor as the leader of Islam. As it turned out, it would be some 24 years before Ali would become Caliph, and in that time, a sizeable group of partisans formed around the charismatic and passionate man. Ali's election and rule turned out to be very tumultuous, and he was murdered during the 5th year of his reign.
Upon the assassination of Ali, after a short period of disorder the Caliphate was reorganized under the rule of Mu'awiyaa who established the Ummawiyy dynasty. Mu'awiyaa's rule brought many innovations and the old partisans of Ali formed the nucleus of the opposition. Ali's eldest son Hasan came to an accommodation with Mu'awiyaa, and it was not until his death and the rise of Ali's second son, Husayn to leadership of the Shi'i faction that the split occurred.
Upon the death of Mu'awiyaa in 680 AD, hoping to make his claim to the Caliphate, Husayn left Medina for Kufah. He was trapped in the desert at Karbala by the soldiers of Yazid, son of Mu'awiyaa and the new Caliph. Without water and hopelessly outnumbered, Husayn and his followers fought a desperate battle and Husayn and many followers were killed. From this point on the Shi'i became alienated, and with a few exceptions were persecuted by Yazid and succeeding Caliphs.
As the main tenant of the Shi'i is the illegitimacy of the Caliphate after Ali, over the next few centuries the Shi'i cause drew many supporters from among the disaffected in the Caliphate, frequently among those not of Arab origin, who were considered second class citizens. Of greater significance was the use of the Shi'i cause as a rallying point for opposition, uprisings, and rebellions. Aside from many failed rebellions, the Shi'i played critical roles in ending the Ummawiyys dynasty, and the Shi'i Buwayhid, a Persian dynasty, controlled the Abbasid Caliphate for over 100 years. Competitors to the Baghdad Caliphate, the Fatimid dynasty centered in first in Tunis and then Egypt and the Almohads in the Maghreb were likewise Shi'i. More dramatically, the Nizari Cult of the Assassins, founded by Hasan Sabah and centered at the mountain fortress of Alamut, terrorized both Christian and Muslim leaders during the Crusades and gave Europe the word assassin (corruption of Hashish, which was used in their rituals).
However, the fortunes of the Shi'i were very precarious until their establishment as the state religion of Safavid dynasty in Persia in the 16th century. From this point on, the Twelver Shi'i received significant support, protection and funding from the Persian state, and major theological centers were built up in Esfahan, Najaf, Qom and Mashad. It has been particularly since the 16th century that the Twelver Shi'i have become the dominant Shi'i sect and developed a very distinct character from the Sunni majority. It has also been since the 16th century that the Twelver cause has taken on a strong identification with Iranian foreign policy, with Twelver minorities looking to Iran for support and Iran viewing Twelver's abroad as it's clients.
In the first few centuries of the Islamic era, any of Ali's descendents, the Alid's, where considered acceptable candidates to be leaders of the Shi'i, but as time went on it became more important for the Shi'i leader to be descended from Ali through Husayn along a designated line. Unlike the Sunni, the Shi'i normally use the term Imam to refer only to Ali and those descendents of his who led the Shi'i faction. The most significant divide among the Shi'i today is among those recognizing 12 Imams known as Twelvers, and those recognizing 7, known as Seveners, or more commonly Ismailis, after Ismail, their seventh Imam, and the Zayyidi who differ after the fourth Imam, and who accept any Alid who is learned and who asserts his rule through force of arms.
A significant feature of Twelver Shi'i belief is in the expectation of the return of the last Imam, called the Mahdi, to lead the faithful in establishing the Shi'i belief on Islam in preparation for the Judgement Day. Other features with roots in Judeo - Christian tradition are the focus on the trials of the martyrs (rawda kani) and exultation of martyrdom in general, the use of self-flagelation as part of religious ritual and the commemoration of the 10 days ending in the events of Karbala (ta'ziya) which are the central event of the Shi'i calendar and bear significant similarities to the passion of Christ. One Shi'i innovations is the permissible use of pragmatic dissimulation (taqiyya), that is, the denial of faith in public, while maintaining it in private. Another innovation is the principle of temporary marriage (mut'a), in which a marriage contract can be entered for a set time, for every period of time between 1 day and 99 years. The woman entering the mut'a, is paid a set amount of money. According to some Shi'i traditions, a man performing 4 mut'as, is secured a place in Paradise. With the Iranian revolution, the system of mut'a was reinstalled as a part of the total Shi'i Muslim practice.
While the Sunni view the Shi'i as innovators, introducing new and unorthodox elements into Islam, the Shi'i view themselves as the true fundamentalists of Islam by retaining the leadership of Muhammad's household. This dilemma can be understood in the context of the methods with which the early Muslims sought guidance in matters not explicitly covered in the Koran. The Shi'i relied on the opinions of their Imams, who as descendents of Muhammad and Ali were viewed as having a closer connection to the divine. The Sunni relied on traditions based in theological and juridical schools and involving analogies drawn from the Koran and Hadith, as well as from the consensus of theologians where analogies were not possible.
The four Imams agreed upon by almost all currently existing branch's of Shi'i Islam are Ali, Hassan, Husayn, and Ali Zayn l'Abidin. The Zayyidi of northern Yemen then recognize Ali Zayn l'Abidin's son Zayyid, after which they recognize a multitude of Imams in different times and places. The most significant line of Imams was founded in Yemen in 893 AD and lasted until the 1960's.
The Ismailis and Twelvers both recognize Muhammad al Baqir, and Jafar as Sadiq, after which the Ismailis recognize Jafar's son Ismail. The various Ismaili traditions then recognize different lines of Imams which reach down to the present day.
The Twelvers continue with Musa al Kazim, Ali ar Rida, Muhammad at Taqi, Ali al Hadi, Hassan al Askari, and Muhammad al Mahdi, their last Imam, whom they believe to be hidden. The Twelver Shi'i are also sometimes referred to as Rafidi, Jafari, Mutawahi, Qizilbash, Imami, Ithna Ashari, and al Khassa. Some offshoots of Shi'i Islam include the Druze, Nusayri, and the Baha'i.
About 10% of the population in Turkey are Shi'i.