In the early 1950s, Iran had a liberal prime minister who was nurturing a delicate and imperfect democracy, and who believed the nation should stop shipping the country's resource riches offshore.
Mohammad Mossadegh wanted to take the wealth buried in Iran's oil fields and invest it into the country and its people.
The parliament that elected him had also passed his flagship legislation, but locking United States and British interests out of the Iranian oil industry was not going to work for the West.
When Mossadegh nationalised Iran's oil industry, he achieved one of his greatest ambitions, but he also set in motion his eventual downfall.
The Anglo-Iranian Oil Company started drilling Iranian fields early in the 20th century and had made its British owners a fortune. That company would later become British Petroleum, now known as BP.
That oil extracted from Iran was largely buying the standard of living enjoyed by Britons, and Mossadegh wanted to change that.
In a now-declassified CIA document, the agency said Mossadegh was "one of the most mercurial, maddening, adroit, and provocative leaders" American and British officials had ever encountered.
His agenda put a target on his back and he soon became the focus of a covert intelligence operation said to have been hatched in the bowels of the US embassy in Tehran.
The Western powers were orchestrating an uprising against him and planned to install a replacement who would be much more friendly to their oil interests.
In that same de-classified document, the CIA admits to Operation Ajax and that it "had a hand" in the demonstrations that spilled onto the streets of Tehran.
MI6 has been much less forthcoming with any admissions, but it is widely understood that British agents were involved in inciting the protests.
While that was happening, the US applied pressure to Mohammad Reza Pahlavi — the man who history now records as the last monarch of Iran.
They wanted him to sign the royal decrees to sanction the change of government.
"The shah … kept on telling the Americans and the British that he couldn't go against oil nationalisation and Mossadegh, because if he did that, he would lose all credibility, he would destroy his monarchy, his throne," said Ervand Abrahamian, emeritus professor of history and middle eastern studies at CUNY Graduate University in New York.
"The final threat that the Americans gave him was 'we're going to go with the coup. If you don't come with us, one of your brothers will replace you'.
"So it's a mafia type of argument and it was at that point, basically, he gave in, but knowing that he was actually undermining the monarchy."
On August 15, 1953, that pressure applied by Western powers reached critical mass and Mossadegh was removed from power.
The streets of Tehran were flooded with those involved in the uprising, but his supporters too, in clashes that killed more than 300 people.
"From then on, people said, if you have freedom and these openings, [a] parliamentary system, it's easy for foreigners to basically use the system to overthrow governments," Dr Abrahamian said.
The public knew there was neither an independent government nor a loyal monarch, and what was left was a "vacuum of legitimacy"; one that would eventually be filled by revolution and clerical rule.
In the decades that followed the 1953 coup, Iran developed nuclear capacity and as the battle for supremacy inside the country continued, that program was growing in size and sophistication.
This week, as Donald Trump repeated his line that Iran could not have a nuclear weapon, he made a threat, saying the US knows where the supreme leader of Iran, Ayatollah Ali Khamenei, is hiding.
Mr Trump is weighing up whether the United States will enter the Israel-Iran conflict directly, saying "I might do it, I might not", and speculation has been building about whether he wants to see a regime change in Iran.
But history shows that a regime can change, but Iran's "red line" on its nuclear program is unlikely to do the same.
Iran's last monarchy
Once Mossadegh was gone, the nationalisation of the oil industry was reversed and the shah allowed a deal between multinational oil giants.
Mossadegh had tried to stand up to the British empire over oil and that made him wildly popular. Some of that support had waned by 1953, but his ousting was a defining moment for Iran.
"That was a moment of deep disappointment and disillusionment for this kind of young, idealistic generation of Iranian liberals, of 1950s modern middle-class Iran," said John Ghazvinian, historian and author of America and Iran: A History from 1720 to the Present.
"They never forgave the United States for it."
The shah of course stood to benefit from being the power centre in the nation and a friend of the West.
Experts agree there had been no love lost between the shah and Mossadegh and now the monarch was both reaping the benefit of his move against the nationalist, but also sowing the seeds for the revolution that was to come.
"The shah was never a huge fan of Mossadegh. The shah was a notoriously insecure person, didn't like prime ministers who were seen as more powerful than himself or more competent than himself," Mr Ghazvinian said.
But as the shah had predicted, while the global oil industry may have recovered, his standing among his subjects did not.
Dr Abrahamian said the shah was now seen as a "puppet" and any hopes for the fledgling Iranian democracy were extinguished.
"It wasn't a perfect democracy, but there was an open system. That ended after 1953," he said.
"The monarch was seen as now a puppet of foreign powers, but I think even more seriously, he undermined the constitution."
The shah would rule over Iran for almost another three decades and it is during this period that Iran's nuclear program began.
The shah and US president Dwight Eisenhower signed a nuclear cooperation agreement, a research centre was established at Tehran University and when the Treaty for the Non-Proliferation of Nuclear Weapons (NPT) was opened for signatures in 1968, Iran signed on the very first day.
The relationship between the United States and the shah was good, and so Iran was brought into the nuclear fold with the promise of "Atoms for Peace".
But the promises made when the US had its man safely tucked inside the grounds of the sprawling Iranian royal estate, would end up needing to be kept by a hardline Islamic regime.
Religious cleric and Islamic leader Ayatollah Ruhollah Khomeini had been living in exile in Iraq and France and he had been making some promises of his own.
Dr Abrahamian said with a vacuum of legitimate leadership in Iran, Khomeini started to offer himself up.
"A guy comes along and says, 'it doesn't matter what was done in the past. I speak for God or I speak for history or I speak for providence. His argument was Islam has the solution, Islam will solve all the problems," he said.
"He actually quite cleverly, very Machiavellianly, said he didn't want to create a new autocracy or a new clerical state — he wanted purely democracy, everyone would have the rights, there would be respect.
"He gave all basically the right lines to both the country and to the public. He had a plan for a clerical state, but he never revealed that."
The 1979 revolution
The shah tried to salvage his reputation domestically, but many Iranians still held a grudge against the United States and he couldn't distance himself from Washington — it was his ticket out of town should he need it.
Mr Ghazvinian said by 1979, Iranian society was fractured and "the centre couldn't hold".
"The centrist liberal nationalists hated the shah because he was a dictator. The Marxists hated him because he was a bourgeois, pro-Western leader. The religious radicals hated him because his rule was seen as very decadent and sinful and not very Islamic and overly pro-Western," he said.
"What made it worse was that all three of those groups had their own reasons to either dislike or be suspicious of, or actually overtly hate, the United States.
"They put a stop to Iran's democratic transition and they were still angry about that."
In December, 1978 it's estimated 2 million people participated in anti-shah protests and by January 16, the shah and his family took that flight out of Iran, never to return.
The shah's son, Crown Prince Reza Pahlavi, lives in exile in Washington DC to this day.
At the time, the Washington Post reported the imperial family, including 63 princes and princesses, fled Iran and were sustained by wealth stashed away in foreign bank accounts.
On February 1, 1979 Ayatollah Khomeini descended from a chartered Air France Boeing 747 and the revolution took hold.
Khomeini and his successor Iran's current Supreme Leader Ayatollah Ali Khamenei led the nation and its 90 million people into the depths of a hardline, authoritarian regime.
The Islamic Republic founded by Ayatollah Khomeini nearly 50 years ago is now very hard to know.
While military leaders want to know every detail of Iran's nuclear capacity, humanitarian organisations struggle to document what they believe to be human rights violations being committed against Iranians, particularly women and girls.
The UN has found there to be a "violent repression of peaceful protests and pervasive institutional discrimination against women and girls" in Iran.
The White House press secretary Karoline Leavitt said Iran could manufacture a nuclear bomb within weeks, but that contradicts what US intelligence said just months ago; nuclear experts say it would likely take much longer.
Iran denies it is attempting to build a nuclear weapon.
As world leaders and intelligence experts contemplate whether this moment is another defining one in Iran's history of leadership struggles, experts warn a change of regime might not deliver a shift on nuclear policy or current sentiments towards the West.
The potential for regime change
In the 1950s, Mossadegh was willing to pay the ultimate price for his nationalisation dream — for the right of a sovereign nation to be the one to profit from its own resources.
Mr Ghazvinian said the current regime had the same absolute beliefs about its nuclear program, in particular about enrichment.
"They see it the same way. It's a national right, and it's simply not something that can be compromised on," he said.
"When Donald Trump says zero enrichment, that's a complete non-starter for Iran, because that is asking Iran to be held to a standard that … no country that's a member of the NPT is held to. Countries that belong to the NPT have a right to enrich uranium for peaceful purposes. Now the problem becomes, is Iran doing this for peaceful purpose or not?"
Mr Ghazvinian said a regime change was unlikely to shift that position because between the "reformists or moderates or pragmatists or hardliners, there is not a lot of daylight between them in terms of the actual red lines on Iran's nuclear program".
He said the likely only way the country would change its position was if it was plunged into political chaos.
"If you instigate regime change and it's replaced either by such an extraordinarily chaotic situation or a civil war, or it's replaced by a regime that is extremely compliant, that is literally a puppet regime of the West, which seems like an unlikely outcome," he said.
Andrew Thomas, a lecturer in Middle East studies at Deakin University, said in a piece for the Conversation any new political leadership being more friendly to Israel and the West was not a foregone conclusion.
Mr Ghazvinian said:
"You could bring about regime change today in Iran, but whatever regime replaces it is still going to take the same approach on the nuclear issue. That's not an Islamic Republic issue, that's an Iran issue."
