The original split between Sunnis and Shiites occurred soon after the death of the Prophet Muhammad, in the year 632.
"There was a dispute in the community of Muslims in present-day Saudi Arabia over the question of succession," says Augustus Norton, author of Hezbollah: A Short History. "That is to say, who is the rightful successor to the prophet?"
Most of the Prophet Muhammad's followers wanted the community of Muslims to determine who would succeed him. A smaller group thought that someone from his family should take up his mantle. They favored Ali, who was married to Muhammad's daughter, Fatimah.
"Shia believed that leadership should stay within the family of the prophet," notes Gregory Gause, professor of Middle East politics at the University of Vermont. "And thus they were the partisans of Ali, his cousin and son-in-law. Sunnis believed that leadership should fall to the person who was deemed by the elite of the community to be best able to lead the community. And it was fundamentally that political division that began the Sunni-Shia split."
The Sunnis prevailed and chose a successor to be the first caliph.
Eventually, Ali was chosen as the fourth caliph, but not before violent conflict broke out. Two of the earliest caliphs were murdered. War erupted when Ali became caliph, and he too was killed in fighting in the year 661 near the town of Kufa, now in present-day Iraq.
The violence and war split the small community of Muslims into two branches that would never reunite.
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