It was in the 7th century of the Christian Era many of the events which shaped the course of Islamic sectarianism occurred. The major one you are aware of is the Shia-Sunni split; the reality of the origins of this schism and the way in which in manifests today is more complex than the cartoon cut-out you are normally presented, but I want to focus on a group which is outside of the Shia-Sunni dichotomy, the Ibadi. The Ibadi are descended from one of the assorted Kharijite sects. The Kharijites were extremists in the early history of Islam, they rejected Ali because he offered to parlay with the opposition. Though analogies are fraught with misrepresentations, the Kharijites are somewhat like the radical Protestants of the early Reformation era; they rejected the the vast majority of Muslims as infidels and refused to compromise with the world. Here is the Wikipedia characterization of Kharijites:
They believed that anybody who commits a grave sin is no longer a Muslim and is subject to excommunication, warfare and death unless the person repented. They believed that the leader of the Muslim community can be any good Muslim, even a slave, provided that he had the community support, in contrast to the dominant opinion among Muslims at the time that the ruler should be a member of Muhammad’s tribe, the Quraysh. Having a strong emphasis on the need to depose unjust rulers and believing that the current leaders of the Muslim community were guilty of grave sins, they withdrew themselves from the rest of the Muslim community, started camping together and waged war against their perceived enemies. They believed that they are the people of God fighting against the people of evil.
So what are the Ibadis like today, the last descendants of the Kharijite movement? There is one state where they are a majority, Oman. From the entry on Oman in the State Department’s Religious Freedom Report 2007:
Apostasy is not a criminal offense under Omani law. Citizens who convert from Islam to another faith, however, generally face problems under Oman’s Personal Status and Family Legal Code, which specifically prohibits a father who leaves the Islamic faith from retaining paternal rights over his children. The law does not prohibit proselytizing, but the MERA will stop individuals or groups from engaging in it if the Ministry receives complaints. The Government uses immigration regulations and laws against harassment to enforce the Ministry’s policy. Article 209 of the Penal Code assigns a prison sentence and fine to anyone who publicly blasphemes God or His prophets, commits an affront to religions and faiths by spoken or written word, or breaches the peace of a lawful religious gathering; this could be used to limit religious expression. However, there were no reports of any prosecutions under this statute during the reporting period. The Ministry reviews all imported religious material for approval.
This is all rather mild compared to many Islamic nations. Here’s the entry on Hinduism in Oman:
Oman may be the only country in the Middle East which has an indigenous Hindu minority. The number of Hindus have declined in the 20th century although it is now stable. Hinduism first came to Muscat in 1507 from Sindh. The original Hindus spoke Kutchi language. By early 19th century there were at least 4,000 Hindus in Oman, all of the Intermediate merchant caste. By 1900, there numbers plummeted to 300. In 1895 the Hindu colony in Muscat came under attack by the Ibadhis. By the time of independence only a few dozen Hindus remained in Oman. The historical Hindu Quarters of al-Waljat and al-Banyan are no longer occupied by Hindus. Hindu temples once located in Ma’bad al Banyan and Bayt al Pir, no longer exist. The only active Hindu temples today are the Muthi Shwar temple located in Al-Hawshin Muscat, the Shiva temple located in Muttrah, and the Krishna temple located in Darsait. The only Hindu crematorium is located in Sohar, northwest of Muscat. The most prominent indigenous Hindus are Khimji Ramdas, Dhanji Morarji, Ratansi Purushottam and Purushottam Toprani.
I think it is illustrative that there are Hindu temples in Oman. My point is covering this somewhat obscure and pedantic sidelight of history is that you can’t predict the future linearly from the parameters of the past or present when it comes to human societies. Whereas the Kharijites were the most prone to declare other Muslims infidels and apostates, the modern Ibadis are among the most tolerant of Islamic sects.