Read this last night while reading the History of Islam for my own edification.. I did not realize the split between Sunnis and Shi'a's goes back all the way to when the Prophet died.
The Sunni-Shi'a split in Islam started with Prophet Muhammad death in 632, which was followed by a dispute over who was to lead the Muslim community, and how the leader was to be chosen. Although the Prophet had said several times, most notably in a famous speech delivered at his last pilgrimage, that Ali was to succeed him as leader of the Muslim community, a gathering of Muslims at Saqifah gave their allegiance to Abu Bakr, as the first caliph after they felt his old age would be a wiser choice than the young Ali. Sunnis also claim that the prophet himself chose Abu Bakr becaue Abu Bakr had led prayers in the prophet's mosque in the last few days of the prophet's life. Sunni Muslims accept Abu Bakr as a righteous and rightful caliph. Shi'a Muslims believe that the prophet had appointed his son-in-law Ali ibn Abi Talib as his successor and that in following Abu Bakr, the Sunni Muslims had strayed from the true path.
I think Islam is too complicated and too big a project for me to read everything about... I'm going to start with Iran - am reading 3 different books on Iran currently but more about that elsewhere... but here is a quick synopsis of the three main sects of Islam
SunniThe Sunni are the largest group in Islam. In Arabic, as-Sunnah literally means principle or path. Sunnis and Shi'a believe that Muhammad is a perfect example to follow, and that they must imitate the words and acts of Muhammad as accurately as possible. Because of this reason, the Hadith in which those words and acts are described are a main pillar of Sunni doctrine.Sunnis recognize four major legal traditions (madhhabs): Maliki, Shafi'i, Hanafi, and Hanbali. All four accept the validity of the others and Muslims choose any one that he/she finds agreeable to his/her ideas. There are also several orthodox theological or philosophical traditions (kalam).
Shi'aShi'a Muslims, the second-largest branch, differ from the Sunni in rejecting the authority of the first three caliphs. They honor different accounts of Muhammad (hadith) and have their own legal traditions. Shi'a scholars have a larger authority than Sunni scholars and have greater room for interpretation. The concept of Imamah (leadership) plays a central role in Shi'a doctrine. Shi'a Muslims hold that leadership should not be passed down through a system such as the caliphate, but rather, descendants of Muhammad should be given this right as Imams.
SufismSufism is a spiritual practice followed by both Sunni and Shi'a. Sufis generally feel that following Islamic law or jurisprudence (or fiqh) is only the first step on the path to perfect submission; they focus on the internal or more spiritual aspects of Islam, such as perfecting one's faith and fighting one's own ego (nafs). Most Sufi orders, or tariqas, can be classified as either Sunni or Shi'a. However, there are some that are not easily categorized as either Sunni or Shi'a, such as the Bektashi. Sufis are found throughout the Islamic world, from Senegal to Indonesia. Their innovative beliefs and actions often come under criticism from Wahhabis, who consider certain practices to be against the letter of Islamic law.