Article : Between Sunni and Shia

Regarding the conflict at Iraq, I think this article should enlite our
knowledge.

Sunni Islam, one of the two main branches of Islam. Shia Islam is the other.
Sunni Muslims constitute the vast majority in the world Islamic community
(see Islam). The term sunna means the "way" or the "example" and refers to
the example of the Prophet Muhammad. All Islamic groups and sects, however,
accept the Sunna, along with the Qur'an (Koran), the sacred scriptures of
Islam, as binding. Because it means the "way," the term sunna may also be
intended to distinguish mainstream Muslims from Shia Muslims, who follow a
side path.

The two main branches of Islam differ primarily in their beliefs about the
succession to Muhammad. Sunni Muslims believe that Muhammad intended that
the Muslim community choose a successor, or caliph, by consensus to lead the
theocracy (earthly kingdom under divine rule) he had set up. Shia Muslims,
also known as Shias, believe that Muhammad chose his son-in-law, Ali, as his
successor, and that only the descendents of Ali and his wife, Fatima, were
entitled to rule the Muslim community. There are also differences between
the two branches in interpretation of the Qur'an.

The doctrines of Sunni Islam were formed toward the end of the 9th century,
and its theology was developed as a complete system during the 10th century.
Both developments occurred, in large measure, as reactions to early
schismatic movements, such as the Kharijites, Mutazilites, and Shias. The
inclusive Sunni definition of a Muslim, for instance, was conceived in
reaction to the narrow extremism of the Kharijites. The strong Sunni
emphasis on God's power, will, and determination of human fate developed in
reaction to the Mutazilite insistence on the absolute freedom of the human
will. Sunni political doctrines emerged in the struggle against the
legitimism espoused by the Shias in the dispute over the succession to
Muhammad (see Caliphate). Various nuances of interpretation and different
schools have developed within Sunni theology, the Sunni tendency having been
to accommodate minor differences of opinion and to affirm the consensus of
the community in doctrinal matters. Four schools of law also developed in
the Sunni tradition: the Shafi'i, the Hanafi, the Maliki, and the Hanbali.