I was doing my own research on the topic of the Shiite-Sunni split. Historically the idea of Shiite was entirely the Iraqi phenomenon. But how come it became Iranian phenomenon when Iran was kind of the backbone of Sunni Islam. Some of the greatest theologian e.g. Imam Al Gazzali, Imam Bukhari, Imam Muslim, Imam Al-Tirmidhi are Iranian?
Even, Sibawayh, who is considered to be the founder of Arabic Grammer, was Persian.
How is now Iran is a Shiite state?
It goes back to one incident, which is the Safavid dynasty. Yes, it was a political issue. The Safavid empire came into the power in 1500. Ismail Safavid who was a Sunni Muslim and the founder of the Safavid Empire. He wanted to break away from the Ottoman Empire. But as you know, technically, in the Sunni Islam, there should be only one Khalifa. Therefore, for the sake of politics, he converted himself to Shiite and then started a brutal campaign to convert the Iranian people to Shiite.
Mughal Emperor Akbar wanted to change the religion and Safavid did change it for the sake of politics.
Apparently, everything is right in politics.