I thought the madness started when the Safavis invaded Persia, did a Holocaust of the Sunni Persian majority, ethnically cleansed the rest, and after the Ottoman Caliph tried to invite them to a peace conference, invaded Mesopotamia and massacred the Sunni population of Baghdad, and desecrated the tombs of Imam Abu Hanifa (A.S) one of the four great ulema of the Sunnis and Sheikh Abdul Qadir Jilani (A.S.) the famed Sufi mystic.
Safavid conversion of Iran to Shia Islam - Wikipedia, the free encyclopedia
Of course we could begin sooner and discuss how after the 'revolution', the first thing Khomeini did was declare Sunni Persians not to have the same rights as Shiites, and killed most of the leaders of the Sunnis
including those Sunnis who had supported him.