Cairo and Al-Azhar
The Fatimids, a Shia dynasty, took Egypt and founded Cairo as a rival capital to Sunni Baghdad, complete with its own caliph. They built al-Azhar as a mosque and teaching institution in 970; it has taught continuously ever since and is often called the oldest running university on earth. Fatimid Cairo grew rich on Red Sea and Mediterranean trade and was notably tolerant of its Christian and Jewish populations. The Sunni–Shia split had produced two competing centres of the Islamic world, each claiming to be the legitimate one.
A belief system rises, spreads, institutionalizes, and then schisms — changing the rules people accept as legitimate.