I came across an interesting paper

The Role of Hadith as Cultural Memory in Shi'i History by RAINER BRUNNER

I can't figure out how to save it on the computer. They probably don't want you to do that anyway. The complete paper is available online for reading so it doesn't really matter.

The central theme of the paper is about the Safavid Dynasty in Iran.

Briefly

• The Safavids were a Shafii Sunni Sufi Order founded by Safi al-Din
• Establish Shia Imamiah as the state religion
• Performed openly the practice of tabarra (disassociating from the three caliphs; Abu Bakr, Umar, Uthman) and publicly cursing their names
• Safavid's main rival was the Turkish Ottoman Empire (Guardian of Sunnism)
• Shah Ismail II of the Safavid reversed the action of his predecessors and forbid the cursing and reviling of the Sunni companions. He tried to revert the empire to Sunnism but didn't succeed.

The author posed an important question about the Safavid's belief system
Did the Shah (King) Ismail, the conqueror of vast lands, adhered to a right form of Shiism (Twelver Shiism)?

Moving on, the author posed another question.
How is it possible to convert an entire country to Shiism, when two third of its population was originally Sunnis?

The Safavid ruled Iran and neighboring areas for 200 years and in that short period of time, they managed to promote a sustainable version of Shiism. Even the Sunni Afghani dynasty that ruled later on couldn't erase Shiism from Iran.

So, what exactly made Shiism so sustainable?
You won't know until you read the paper.

Reference