>>510841648 (OP)Burgers, CIA and Mossad happened.
https://en.wikipedia.org/wiki/1953_Iranian_coup_d%27%C3%A9tat
Since Iran wanted to put their oil reserves under state control (undoing privatizing) in the 1950s, the CIA with help of the Mossad overthrow the Iranian government. Which has been - in comparison - way more liberal than the Mullahs.
Internally Iran never really recovered politically with its people, a tension that grew until 1979 when the radical Mullahs took over during the (Islamic) Iranian Revolution.
In very short.