One can wonder what is going on in the Middle East these days, especially the civil and sectarian strife that are  tearing Iraq, Syria and Yemen apart.

In the latest development, Sunni Saudi Arabia on Sunday severed ties with Shia Iran over the execution of a Shia cleric. A number of Saudi Arabia's Sunni allies have joined diplomatic action against Iran after a crowd set alight Saudi embassy in Tehran.

To understand these conflicts, one need to know the history of Islam. Within the House of Islam ancient antagonisms between Sunni and Shia Muslims are alive which are sometimes overlooked.

After the 1979 Iran revolution, Saudi Arabia, which claims the leadership of Sunnis, has increasingly adopted a muscular role in the conflicts in mainly Shia-dominated regions and Iran, which claims the leadership of Shias, has vowed to do whatever necessary to protect the Shias in the region.

But the root of these conflicts goes back to events that took place in 632.

Indeed, the factions that we call Sunnis and Shias trace the great divide between them to the seventh century and the aftermath of Prophet Muhammad's death. They claimed that Ali, prophet's son-in-law, was the rightful successor to Muhammad (pbuh) as leader (imam) of the Muslim community following his death in 632. Instead Ali was the fourth, and was assassinated in 661 after a five-year caliphate. His sons, Hassan and Hussein, were denied what they thought was their legitimate right of accession to the caliphate. Hassan is believed to have been poisoned in 680 by Muawiyah, the first caliph of the Sunni Umayyad dynasty, while Hussein was killed on the battlefield by the Umayyads in 681.

This initial rift was compounded over the centuries by a recurring pattern of struggle within Islam between strains of militant puritanism and the less rigorous attitudes of various ruling classes. Such a puritanical ideology arose within Sunni Islam in the fourteenth century, exemplified by the teaching of a formidable Syrian scholar, Ahmad ibn Taymiyya. His doctrine, though popular among many Muslim Arabs in his lifetime, placed him at odds with Muslims of a more laxist point of view.

In the eighteenth century in the Arabian peninsula, the reformist teacher Muhammad ibn 'Abd al-Wahhab used the rigoristic ideas of Ibn Taymiyya to fashion the tradition of strict interpretation of Islamic texts usually called "Wahhabism" by non-Muslims today. To propagate his ideology, Ibn 'Abd al-Wahhab collaborated with the sheikh of an obscure village in north central Arabia, Muhammad ibn Sa'ud, and between them they imposed unified rule and their new, rigoristic version of Islam throughout the Arabian peninsula. Muslim legal scholars belonging to the family of Ibn 'Abd al-Wahhab continue to the present day as religious and legal advisers of the House of Sa'ud, the ruling family of Saudi Arabia, the presumed leader of the Sunni Muslims.

After the deaths of Ali and his sons, his devotees, who believed him to be the rightful caliph, created what came to be called the Shia Imamate on a grand scale that grew in religious significance over the two centuries. Indeed the descendants of 'Ali to the ninth century are all believed by Shias to have died as martyrs, victims of oppression by the Sunni caliphate.

One can trace a line from these distant events and antagonisms, with their churning reversals of fortune, to the conflicts of today. At the death of the eleventh Imam in the Shia lineage, Hasan al-'Askari, it is said that allies of the Imamate hid his little son from Sunni enemies. Calling themselves the representatives of the Hidden Imam, four of these allies in succession governed the Shia community on behalf of the Hidden Imam for seventy years. Eventually a military upstart dynasty, the Buyids, originally based in Iran, took on the ideology of representing the Twelfth Imam and imposed themselves in 945 as his representatives -- and as the overlords and protectors of the Sunni caliphate based in Baghdad. Such Shia military supervision of the Sunni caliphate reduced the caliphate to a puppet dynasty, with only a few partial returns to genuine political power in subsequent centuries. Sunni resentment of Shias even today consciously or unconsciously recalls this humiliation.

Representing the Twelfth Imam has provided many subsequent Shias with a symbol for their political aims; the most recent representatives in Iran have been the Imam Ruhollah Khomeini and his successor, Ayatollah 'Ali Khamenei.

The fight for the leadership of Muslim world is still very alive. Until the 1960s and 70s, Saudi Arabia and Iran were uneasy allies regarded as the "twin pillars" of Washington's strategy to curb Soviet influence in the Gulf. Sectarianism was muted.

But rich on its new oil wealth, Saudi Arabia began to propagate its rigid Salafi interpretation of Sunni Islam which regards Shi'ism as heretical, in mosques around the region during the middle of the last century. And, after its 1979 revolution, Iran adopted - and exported - the doctrine of Velayat-e Faqih, which says ultimate temporal power among Shias should reside with its own supreme leader.

That growing ideological divide set up a simmering mistrust that was soon matched by a geopolitical rivalry that has driven their fractious relations for the subsequent 37 years. The death of the cleric just happened to be another incident that may only fuel one of the most ancient rivalries in history.

Who are the Sunnis?

The name "Sunni" is derived from the phrase "Ahl al-Sunnah", or "People of the Tradition". The tradition in this case refers to practices based on what the Prophet Muhammad said, did, agreed to or condemned. All Muslims are guided by the Sunnah, but Sunnis stress its primacy. The great majority of the world's more than 1.5 billion Muslims are Sunnis. In the Middle East, Sunnis make up 90% or more of the populations of Egypt, Jordan and Saudi Arabia. Sunnis regard themselves as the orthodox branch of Islam.

Who are the Shias?

In early Islamic history, the Shia were a movement - literally "Shiat Ali" or the "Party of Ali". They claimed that Ali, prophet's son-in-law, was the rightful successor to Muhammad (pbuh) as leader (imam) of the Muslim community. Instead Ali was the fourth caliph, and was assassinated in 661 after a five-year caliphate. His sons were also denied the leadership. Shia Muslims are in the majority in Iran, Iraq, Bahrain, Azerbaijan and, according to some estimates, Yemen. Shias constitute about 10% of all Muslims.