It really stems back to the 1950s, SoA2. Iran was, for all practical purposes, occupied by the Allies after WWII, without being an enemy. The British and the US had two purposes: They wanted the oil and its location as a buffer and place to monitor (spy) on the Soviet Union.
The British, as they had done in other oil colonizations of Arab nations, wanted the oil, but didn't want to actually
pay for it, or share the revenues with countries or people whose land it came from. They just took it (well, they paid about 1% of the going rate) by bribing the leaders, and/or installing leaders who would repel uprisings by the people.
Iran was a democracy with a parliamentary government. The Shah replaced his father, who was pretty much a despot. His son was installed, but he wasn't the brightest guy politically. He was prone to indecision and became reliant on deception and strongarm tactics to maintain power. He knew that the US and the British would butter his bread better than the Russians, so he was easily led.
He was violating the Iranian constitution, since the power was not centered with the King, but with the Prime Minister and parliament. He imprisoned, tortured, expelled and murdered those who wanted Iran to remain a democracy, not a dictatorship, and also Islamic clerics who wanted to maintain their influence over the people also. And they were not 'radical' Islamics, at least not yet. We needed a few years to turn them into radicals.
The CIA and British orchestrated a coup of the premier, who was constitutionally in power, to strengthen the Shah's position. The premier and the people of Iran wanted the British to pay a reasonable amount for the oil and invest more into the building the economy of Iran, than just taking the oil. Negotiations were stalled, until it was realized that it was cheaper to overthrow the premier, than pay a fair price for the oil.
The CIA even went so far as to bomb a mosque to fuel tensions. I know that seems shocking, but, unfortunately, it is how the world works, sometimes.
In the 1960s, many Iranians emigrated to the US to escape the Shah's police state. The US played both sides of the coin - allowing the immigration to maintain a 'humanitarian' public image, while simultaneously helping the Shah remain in power by his brutal means. The problem came when Iranians learned of the double-cross by the US and British a decade later from newspaper reports from leaked CIA information.
Those documents are (reluctantly) unclassified now.
Here>> is the summary.
It's simply amazing how history repeats and repeats. Ironically, it was the NYT that broke the story and fought for decades to get the confirming documents de-classified.
And the ultimate irony is that the CIA conceived and executed a plan to bomb a mosque to give the Shah a plausible excuse to take a hard line against terrorists, who bomb mosques. Unfriggin'believable, isn't it?