In 1953, the CIA orchestrated a coup to oust Iranian Prime Minister Mohammad Mosaddegh (because the British wanted to but couldn't do it themselves, as always), putting Shah Mohammad Reza Pahlavi back in power, ending democracy in Iran. It wasn't the first time, as we also had Shah Mohammad Reza replace his own father, Reza Shah Pahlavi, during World War II. Reza Shah himself was put into power with the backing of the British.
That mellow looking man in the picture was Mosaddegh. For his grand sin of becoming prime minister, he got to spend the rest of his life in house arrest, dying in the 1960s.
Then, in 1979 with unrest growing against the Shah and the US wanting him out because of his role in rising oil prices, we persuaded him to allow Ayatollah Khomeini to come back from exile in France ostensibly as a token of good will towards his people, but knowing very well that that would be the end of the Shah's reign.
The US Government actually seriously believed that in gratitude, Khomeini would now take his turn as the US puppet a charge of Iran. Something about getting tortured before he escaped to France and his father getting tortured to death by the Shah's regime didn't exactly make him overly conducive to being the tool of the people responsible. So he went rogue.
You know the rest.
The world would be an entirely different place if it wasn't for us constantly meddling with Iranian governments.
That's three people we are responsible for taking over that country, one of them twice, but do we ever learn? No, we're going to do the same thing again to further antagonize them.
After 2600 years, the world's second oldest country doesn't forget that easy.