Okay, thanks. Just wondered if there was anything new, other than settling scores.
Settling scores does not capture the character of the divisions.
Check the geopolitical distribution, and who had reason to resist Arabian and Turkish domination; many Shi'ites there.
Being a theologian, I've perhaps overvalued the Shi'ite formal openness to new thought compared to the Sunni freezing of religious development after the first few centuries of Islam (apart from the existence of several major schools of interpretation, which preserved some variety).
The Saudi invasion of the Ottoman Empire and seizure of the Holy Places Mecca and Medina put them in a position to impose a very conservative version of Sunni tradition itself and propagate it worldwide, to the danger of fellow Muslims, both Shi'a and Sunni.
On the five pillars of Islam itself, there is largely agreement, though a Sunni told me that at prayers there are slight differences of movement between Sunnis and Shi'ítes that one can observe if one knows what to look for.
The Yemen situation is partly proxy war between Saudi Arabia and Iran, but don't forget that after the British ceased to rule Aden, it was for many years divided into North Yemen and South Yemen.
Never forget the importance of tribes. Most tribes in Afghanistan are Sunni.
Peace,
Michael
