The degeneration of the Iraq conflict into a low level but nonetheless murderous civil war between Sunnis and Shi'is has highlighted the principal sectarian divide in the Islamic world. However, given the media's pathetic inability to explain the nature of Sunni and Shi' differences in the Islamic world and the reasons why they have become so explosive in Iraq, it is hardly surprising that Americans' understanding of the carnage is largely limited to a sense that most Arabic religious terms begin with the letter S. Yet the sectarian distinctions and violent conflict between these two Iraqi religious communities are recognizable as a typical catalytic reaction that occurs in societies where doctrinal differences interact explosively with socio-economic or political schisms.

A well known contemporary example is the "Troubles" in Northern Ireland, which have plagued that province for the last half-century. Protestants and Catholics there as elsewhere have fundamentally different beliefs about religious authority and other matters, but they have not bombed each other's pubs over the fine points of Christian theology. Northern Irish Christians have been at each other's throats because of the political and socio-economic history of the province. Nor, for all their theological differences, have Sunnis and Shi'is been murdering one another in Iraq because of disputes over how many angels fit on the head of a pin. In Iraq as in Northern Ireland political disputes are the underlying causes of the conflict. And just as the recent power-sharing agreement between the IRA's Jerry Adams and the not Very Reverend Ian Paisley that offers the best chance to bring "Troubles" to an end, so too in Iraq a political solution acceptable to all sides is essential to end the carnage.

All Sunnis and Shi'is accept the fundamental principles of the Islamic faith, beginning with the role of Muhammad, who is revered as the last or "seal" of the prophetic line that began with Moses and continued with Jesus Christ – but only as a prophet and not the son of God. All Muslims accept the Arabic Quran as the revealed word of God to Muhammad, a series of revelations known as surahs or chapters that begins with the verse "In the name of God, the beneficent, the merciful." All Muslims observe the Five Pillars of Islam: 1. The monotheistic profession of faith – "There is no God but God and Muhammad is the Prophet of God," 2. The five daily prayers, 3. Alms-giving, 4. Fasting, and, 5. Pilgrimage to Mecca. ." All Muslims also revere the Prophet's family, the ahl al-bayt, literally the "people of the house." Yet Sunni and Shi'i attitudes to Muhammad's family and descendants are fundamentally different, and these differences are the basis for the development of two Muslim confessional communities.

Sunnis believe that Muhammad (570-632 CE) was the last divinely inspired individual and that the khalifas or caliphs, literally the successors to the Prophet, were simply guardians of the political independence and religious integrity of the newly formed Muslim community. These men were not, Sunnis contend, divinely chosen nor did they possess any special religious insight. In Sunni eyes, these caliphs did not possess, as some Catholic Popes claimed, infallibility in interpreting religious doctrine. Sunnis view the first four caliphs, men who had known or were related to Muhammad, idealistically as the four "rightly-guided Caliphs," (632-661 CE) of an Islamic Golden Age, and most of them also accept the legitimacy of both the two later dynastic Caliphates: the Umayyads (661-750 CE) of Damascus and the 'Abbasids (750-1258 CE) of Baghdad and those who ruled individual Muslim countries afterwards.

Even after the Islamic world fragmented into numerous regional states ruled by autocratic sultans, a process well under way by the 10th century CE, Sunni Muslim political theorists justified the reality before them by arguing that stability trumped religiosity, a rationale not now accepted by al-Qaeda or many members of the Muslim Brotherhood, who believe that Saudi Arabia, Egypt and many other contemporary Muslim state are irretrievably corrupt, decadent un-Islamic autocracies that ought to be replaced by Islamic regimes, such as that of the first four Rightly Guided Caliphs.

Sunnis take their name from the Arabic word sunna, which means tradition. Originally Muslims used the term when they referred to the hadith, reports of the sayings or actions of the Prophet Muhammad or even, sometimes, those of his Companions. Over the course of the two succeeding centuries Muslim theologians came to identity sunna solely with Muhammad and gradually the hadith became accepted as a source of Islamic law that complemented the Quran, Muhammad's divinely inspired revelations.

By the tenth century CE Muslims increasingly used the Arabic term ahl al-sunna to refer to the members of the majority or, in theological terms, the orthodox community. These individuals accepted the authority of scripture as embodied in the Quran and the hadith, and recognized the legitimacy of the caliphs and their successors. Most Sunnis accept only the Quran and the hadith as sources of religious truth and social guidance, and in the twenty-first century conservative or fundamentalist Muslims usually deny the validity of interpretation or philosophically inspired logical analysis of scripture. These Muslims take essentially the same attitude as fundamentalists in other religious traditions, ranging from Christians to Hindus.

Shi'i Muslims differ from Sunnis in that they not only revere Muhammad's family, but attribute unique religious insight to his relatives and descendants. They believe that these individuals possess spiritual charisma, and assert that they rank just below the prophets because they are divinely inspired, not to produce new prophecy, but to understand the true or esoteric meaning of the Quran. In their eyes, therefore, Muhammad's relatives and descendants were the proper leaders of the Muslim community and of the first four caliphs only the fourth, 'Ali, Muhammad's first-cousin and son-in-law, was legitimate. Early in Islamic history, some Shi'i Muslims began to publicly denounce the first three caliphs as illegitimate, an act that was and is deeply offensive to the Sunni community who regard these men as icons of the early Muslim community.