Shia Sunni schism has always acted as principle fault line in Islam. The 1.3 Billion strong Muslim population has been broadly divided into these two principle sects. The rift between the two biggest Muslim factions goes right back to the beginning-and a row over as to who would succeed Prophet Mohamed as the leader of the emerging and naive Islamic community when he died in the 7th Century.
Over the core of the Shia Sunni dispute was an impassioned argument over the principle of succession in the nascent Muslim community. There were 2 major principles which could have decided the successor of Prophet Mohamed and this caused the genesis of a fault line which has turned into a rift today.
Majority of the population believed that there should be a Meritorious Principle of Succession. According to this principle, Abu Bakr, the closest associate of Prophet would be the next successor. This sect or faction of people came to be known as Sunnis.
The other group of people believed in the Dynastic Principle of Succession and said that the Islamic leadership should only be with the family of the Prophet, thus going against the principle of meritocracy. They thought that Prophet’s son in law and nephew Shiat Ali should be the next successor of Islamic community. This faction came to be known as Shias after the name Shiat Ali or “The Party of Ali.”
Over the period, this principle fault line of Shia Sunni was exploited to cause a rift between the Muslim communities. Today, both the sides (Shia Sunni) believe in The Quran but have diverging traditions of rituals, laws and practices. In the beginning, there were more similarities than differences between the two sects, which gradually led to dilution of similarities between Shia Sunni and marking of the differences.