It’s a good column, Dex, but as a non-Muslim I think I could take some issues with it, as a matter of facts and opinion ;). Hopefully I don’t come off as churlish or needlessly pedantic - I understand the issues of space constraints when trying to cover everything.
A factual correction ( I think ). It’s not 100% clear, but you seem to imply of saying that armed conflict broke out immediately with the election of Uthman. That is of not the case - fighting only broke out after Uthman was assassinated in 656. Ali may have resented his election, but he did not raise arms against it. It was Ali’s claiming of the mantle of Caliph in 656 that triggered the fighting and the issues surrounding that, that triggered the first Islamic civil war ( fitna ).
An issue of opinion. I’d say the final Sunni-Shi’a break was the triumph of the Abbasids in 749. Up until that point, Shi’ism was a bit of a catchall category and many who supported any member of the Prophet’s family over the Umayyads were considered Shi’a. When the Abbasids ( descended from Muhammed’s uncle ) took over, this group then merged into the Sunni mainstream. Those that held out only for the children of Fatima, remained as Shi’a.
An issue of phrasing.
Not quite - 80-85% believe there was 12 Imams ( including the occultated one ). The other 15-20% believe there are fewer, hence the religious splits within Shi’ism ( i.e. “Fivers”, “Seveners” ).