A lot of political scuffling around that time, but the story is basically the following:
Protests in 1949 and 1950 succeeded at securing fair elections inside the constitutional monarchy.
Winner in the election and an important opposition leader against the Shah (King) Mohammed Mossadegh was appointed as Prime Minister in 1951.
He implemented a wide array of social reforms, passed a land reform bill and attempted to nationalize the british oil companies. Social democrat stuff.
Britain cut off Irans ability to sell any of the oil on the world market in response, because they didn't want their oil companies nationalized.
This reduced Irans Oil production by 96% and put significant stress on Irans economy, setting the stage for all of the political chaos after.
Mossadegh then calls an election, tries to get the Shah to concede some power to him and then resigns when his request is denied.
Protests and strikes break out eventually leading to Mossadegh getting reinstated and his wishes in 1952. He then introduces a bill to receive emergency powers for 6 months, later 12 months.
He weakens the shah further, makes his land reforms more expansive etc.
The british sanctions hurt his popularity a lot tho and there's also growing opposition because of the authoritarian measures he employs.
In late 1952 Mossadegh cuts of diplomatic ties with Britain.
Eisenhower and Churchill then orchestrate a coup attempt. (Eisenhower made Americas Position shift in favor of intervention) in 1953.
The measures for regime change included propaganda campaigns. Trying to convince the Shah to oust Mossadegh. And CIA operatives pretending to be socialists and nationalists threatening religious groups with "savage punishment" if they oppose Mossadegh.
Mossadegh grabs power with a 99% - 1% referendum to give him emergency powers, which had seperate polls for yes and no.
The CIA already gave up at this point, but the CIA operative Kermit Roosevelt ignored it and successfully ousted Mossadegh by paying protestors and cooperating with royalist troops.
Many supporters of Mossadegh were tried, tortured and killed in the aftermath. #history