When you bring God into politics very strange things happen. You can see this now in both America and Iran - in their elections and also in the growing confrontation between them. But it wasn't always like this - in fact for most of the 20th century fundamentalist religion in both America and Iran had turned its back on the world of politics and power.

But in the 1970s everything changed. For that was the moment when religion was deliberately brought into politics in both countries with the aim of using it as a revolutionary force. And those who did this - Khomeini in Iran, and right-wing activists in America - were inspired by the revolutionary theories and organisations of the left and their ambition to transform society in a radical way.

I want to tell the forgotten story of how this happened - and how in the 1980s both the Americans and the Iranian idealists came together in a very odd way - with disastrous consequences.

In the early 1970s in Washington a small group of young conservative activists came together to try and change American politics. They called themselves the New Right and they were convinced that unless they did something drastic, the liberals and the left-wingers in America were going to take over the country.

One of the leaders of the New Right was a man called Paul Weyrich, and in the wake of the student revolts of 1968 he infiltrated the meetings of left-wing grassroots organisations. He was astonished by the amount of planning and tactics that he saw and he realised that the conservative movement in America was completely unaware of all this. The right, he said, were still trapped by the belief that people would simply vote for them because they were right.

So the New Right set out to organise a new grassroots movement that could counter the left's success. They had all sorts of discussions and during one of them Weyrich pointed out that there were millions of Americans who were socially and culturally very conservative but who never voted. They were the religious fundamentalists and the evangelicals - a vast segment of the population who believed that they should never get involved in politics.

Weyrich realised that if you could activate the fundamentalists and the evangelicals then the New Right could create an incredibly powerful force. But the problem was how to persuade them. The fundamentalists were driven by pietism - the belief that a true Christian should not only devote their life to god, but also turn their back on the secular political world. They should live the good life through their own actions - and forget about politics.

Ironically it was the liberal left that offered Weyrich the way to activate the fundamentalists. Since the late 1960s the left had pushed through reforms on all kinds of moral issues - gay rights, abortion, sexual discrimination. This had shocked the Christian heartland of America because it was politics attacking and undermining the very beliefs through which they lived their private lives.

The final straw came when President Carter abolished the charity status for the fundamentalist religious schools. This really hurt because they thought Carter, an evangelical, was one of them. But Carter was of the old school - he believed that religion should be separate from politics.

So in May 1979 Paul Weyrich and four other young activists drove to the Holiday Inn in Lynchburg Virginia to meet one of the most powerful evangelical pastors in America, Jerry Falwell. Like a number of other pastors, Falwell had his own television network and millions of followers. What happened at that meeting would shatter the pietism of millions of fundamentalist Christians and bring them - and their beliefs - into the heart of American politics.

I interviewed Paul Weyrich and another of the New Right group, Morton Blackwell, about that meeting. Here they are - describing what happened. It begins with Weyrich telling how he infiltrated the left. Weyrich was a fascinating man (he died in 2008) - a conservative revolutionary.

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At the same time - in early 1979 - the Ayatollah Khomeini led a revolution that toppled the Shah in Iran.

Khomeini did this by completely transforming Shia Islam. It was a religion that for hundreds of years had taught its millions of followers to turn their backs on politics and power. Khomeini had turned this upside down - and had brought Shiism into the heart of politics.

Back in 1963 Khomeini was just another conservative cleric living in the City of Qom, but then the Shah launched the White Revolution which was supposed to modernise Iran. Khomeini was horrified because the programme was going to emancipate women, swear in elected officials on any holy book - not necessarily the Koran, and worst of all it threatened to take away the clergy's very large landholdings.

Here's an image of the future of the Shah's revolution. Girls running nuclear power.

But the problem was how to challenge the Shah? Shiite Islam had a quietist attitude towards politics. One of its main ceremonies is "Shiite lamentation", where the faithful ritually flagellate themselves. Throughout Shiite history the clergy have made this the symbol of a retreat from the world - and above all from politics and power. The people must wait in a world full of shadows and evil - for the return of the twelfth imam. This meant that political power was evil and debased, and you must have nothing to do with it.

Khomeini decided to overturn this - and to do it, like Paul Weyrich in America, he turned to the ideas of the political left.

In the 1960s an Iranian sociologist called Ali Shariati had become fascinated by the writings of the Third World revolutionary, Franz Fanon. And when Shariati translated Fanon's writing into Persian he used the language of Islam - so marxist terms like "the oppressors" became "the arrogant" while "the oppressed" became "the weak" or "the disinherited".

For Khomeini this was the key - and in 1970 he gave a series of lectures that took Shariati's attempt to fuse revolutionary Marxism and Islam and used them to portray a new vision of Shia Islam. Your duty, Khomeini said, was no longer to remain passive but to seize power and drive out the wicked and corrupt ruler. It was an extraordinary move, because Khomeini was exploding one of the fundamental ideas of his religion.

You don't just sit around waiting for the Messiah. You fight - and you take power now. Led by the clergy.

Khomeini lifted a lot from Shariati, but it was also driven by his powerful personality and his brilliant use of the media. Here is is film of Khomeini in exile in Paris in 1977 as his ideas were taking hold in Iran. It is followed by some film rushes of the extraordinary mass demonstration that happened in Tehran on the 29th March 1978 - the slogans on the banners show the fusion of left wing revolutionary ideas and Islam. As the Shah says in the film, Khomeini had combined "the red and the black".

A few weeks later violent revolution began - and I have included in the rushes some great and very brave reporting in the midst of the fighting by the BBC reporter Richard Lindley.

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In America the politicisation of religion had taken off in a big way. Throughout 1979 The Revd Falwell travelled the country contacting, he claimed, 72,000 pastors. He showed them how to mobilise their millions of followers and how to register them to vote. Falwell also worked with the New Right to use Direct Mail to dramatise the moral issues - and to provoke.

When gays were allowed to lay a wreath on the tomb of the Unknown Soldier in Washington, Falwell sent out a warning to the Moral Majority followers:

"That's right - the gays were allowed to turn the tomb of the Unknown Soldier into:

THE TOMB OF THE UNKNOWN SODOMITE!"

But the question was - who should the newly radicalised fundamentalists support in the 1980 presidential election? The Religious Right prepared a Presidential Biblical Scorecard which was sent out to millions.

It scored all the candidates on the great moral issues - abortion, homosexuality, national defence, and many others. Jimmy Carter didn't do very well.

But the question was really decided at a dramatic mass meeting in Dallas. It was called The National Affairs Briefing and was sponsored by the Religious Roundtable - a coalition of religious groups. All the candidates for President and other political figures were invited to come and explain their views on religion - but only one turned up, Ronald Reagan.

The meeting's other aim was to show just how many leading pastors now believed that evangelical religion should become involved in politics. Along with Falwell, leading televangelists like James Robison and Jimmy Swaggart whipped up the 17,000 strong crowd in the Dallas Arena - in front of 50 million television viewers.

Other leading pastors, like Billy Graham, refused to come. They hated what was happening. One of them, a Baptist called James Dunn gave a brilliant quote:

"We've got a bunch of TV preachers who want to establish a theocracy in America, and each one of them wants to be Theo."

And then Reagan made his speech.

Here is James Robison at the meeting followed by Reagan, a moment that many in the movement say was the turning point. I have also included Jimmy Swaggart attacking those who say religion should not be involved in politics - because it is really funny and shows just how powerful and confident this movement was back then.

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But as all this was happening in America, the battle that was taking place in the Iranian revolution over religion and politics spilled over into American politics - and things began to get very complicated.

And its victim was the hapless President Jimmy Carter.

Unlike previous US presidents, Carter didn't like the Shah of Iran. The CIA had told him horror stories of what the Shah's secret police were doing to Iranian dissidents. And Amnesty were publiciising the same thing - like the use of bacon slicers to cut off prisoners' hands bit by bit. Carter didn't like this, he believed that America should promote human rights around the world and he publicly criticised the Shah.

But not very strongly. Carter said that criticism of the Shah's secret police was "perhaps sometimes justified", while he continued to give Iran vast amounts of weapons.

In 1977 the BBC were making a sycophantic documentary about the "life of Washington's first lady" - Rosalynn Carter. They were filming in the White House when the Shah of Iran came to visit. Carter had promised he was going to tell the Shah he should try and liberalise his country. Unfortunately thousands of Iranian exiles didn't think this was enough and they turned up outside the White House to protest, and Rosalynn's plans started to go wrong

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When the Iranian revolution happened, President Carter tried to contact what he believed were "the moderates" in the revolution. The embassy in Tehran opened a dialogue with the liberals who had allied themselves with Khomeini - and who now wanted to transform Iran into a democracy. The most important was the new Prime Minister Mehdi Bazargan.

But Khomeini wanted to get rid of these liberals because they were opposed to his idea of the new political structure of the Islamic Republic of Iran - where absolute power would be given to "the Guide", which meant Khomeini himself. The liberals saw this as the restoration of a dictatorship.

So Khomeini and his supporters manufactured a crisis. On November 4th 1979 500 "students in the line of the Imam" (ie followers of Khomeini) stormed the American embassy and took the diplomats hostage. There are stories that a young Ahmadinejad was one of the students, but no one has proved this and he denies it.

There is a great book written by Massoumeh Ebtekar who was one of the invaders of the embassy. She describes how when they began to explore, the students found tons of shredded documents lying discarded on the floor and in the barrels of the shredders. One of the invaders, an engineering student called Javad thought that the shreds from each document must have fallen together - and so it might be possible to rebuild the documents.

"He was a study in concentration - bearded, thin, nervous and intense. These qualities combined with his strong command of English, his mathematical mind and his enthusiasm, made him a natural for the job.

One afternoon he took a handful of shreds from the barrel, laid them on a sheet of white paper and began grouping them on the basis of their qualities.

"After five hours we had only been able to reconstruct 20-30% of two documents. The next day I visited the document centre with a group of sisters. 'Come and see. With God's help, with faith and a bit of effort we can accomplish the impossibe', Javad said with a smile."

A team of twenty students then went to work to reconstruct all the papers - in the end they published 85 volumes of them. The documents revealed the deep and cynical involvement of America in supporting the Shah throughout the 1970s. They were the Wikileaks of their time, for they showed how the CIA had worked closely with SAVAK - the hated and vicious Iranian secret service.

The students renamed the embassy "the nest of spies" - and quite a lot of the hatred and distrust of America that has pervaded Iran ever since comes from those reconstructed documents.

And what's more the documents also helped Khomeini destroy his liberal allies, because they revealed that, since the beginning of the revolution, President Carter had been talking to "the moderates". Khomeini seized on this and used it to force out and arrest all those in the new government who wanted a democracy. They were traitors because they had been corrupted by the Great Satan.

Khomeini then used the embassy crisis - fuelled by the hatred of America - to build his vision of a radical theocracy in Iran. It had an enormous effect on the Presidential campaign in America because it made Carter look impotent, especially when his mission to rescue the hostages failed dramatically with helicopters crashing and burning in the Iranian desert.

To give a sense of the drama and uncertainty of that time - here are some sections from the BBC News Comp tapes of the time - 1979-80. They were the 2-inch video tapes onto which raw material coming over satellite from Washington and Tehran was first dumped. I have kept them as they are - and they give a very good sense of the complexity and dislocation of what was happening. They include footage the Iranian students shot as they invaded, and then some video of what they found inside the embassy - the secret communications equipment, and then they find the shredders.

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In November 1980 Ronald Reagan won the presidential election. Millions of newly radicalised Christians voted for him. Reagan would have won without their votes, but the New Right had awoken a powerful force that now came into Washington - an evangelical conservatism that wanted to change the world, not just keep it the way it was, as traditional conservatives always had.

By 1980 the idea that left-wing politics could change the world was finished and over - throughout the western world. And in a strange way these new conservative radicals were the last spasm of twentieth century revolution - created out of left-wing tactics borrowed by the New Right - and then fused with fundamentalist anger.

But the problem was that almost immediately Reagan ignored them. Although in speeches he paid lip service to their fury over subjects like abortion - he did almost nothing to remake America into the morally good country they sought. And the religious right and their supporters were frustrated and angry.

But they still had hope in foreign policy. Like the fundamentalists, Reagan saw foreign policy not as realpolitik, but as a global battle of good against evil - and he backed the idealists in his administration who wanted to support what they called Freedom Fighters in countries like Nicaragua.

But this would lead the American religious idealists into a very weird situation - they would become the allies of the religious revolutionaries in Iran.

Because Khomeini's revolution was also having problems. The country was facing an economic disaster and the millions of poor people who had created the revolution were finding that their prospects hadn't really changed. While the intellectual leftists who had supported Khomeini had turned against his idea that he should be in charge.

So Khomeini simply annihilated the left. He killed them - or forced them to confess to treachery on TV from prison.

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Then Iraq invaded Iran - and hundreds of thousands of the most devoted and active revolutionary militants were sent off to become cannon fodder. They were giving their lives to defend the revolution - but their deaths also removed the growing threat from this group as Khomeini's revolution failed to solve the economic and social problems.

And by 1984 Iran had become a very dark and strange place. Any idea of using religious energy to change the world was gone - and faced with the appalling butchery in the war, Iranian Shiism found it's way back to the old idea of martyrdom, but in a horrific way.

The historian of modern islamism, Gilles Kepel, described what happened to that young revolutionary generation.

"The appalling butchery of the war against Iraq gave the younger generation of poor Iranians an incentive to return to the former tradition of martyrdom.

No longer at issue was the transformation of the world, for the revolution had clearly failed to satisfy that expectation. Rather the young men developed a new desire - a longing for death - as a response to the failure of Iran's revolutionary utopia and the pressures of the war with Iraq.

The Shiite death wish took on massive dimensions with the sacrifice of the bassidjis at the front. The colunteers wrote letter and last testaments to their families, asserting their longing for death. What these tragic documents describe in religious terms is no less than the political suicide of the young urban poor of Iran in the 1980s."

In 1984 the BBC made a two-part documentary recording this dark, strange Iran. It is a brilliant film - it shows just what Kepel describes, hundreds of young men being bussed off to the front every day, welcoming the fact that they are all going to die.

The giant fountain in the mass war cemetery spouts blood-red water. While in cool, white offices, very young children are taught to embrace the idea of martyrdom by a spooky cleric - and are given toy models of the US space shuttle to reward them. And the revolutionary guards spend their time driving around policing their neighbours' morals, and hunting down ill-veiled women (bad hejabi).

Here are some sections from the film. I really like the way it is made - refusing to bow to the normal hysterical news style. Its calmness evokes the growing darkness brilliantly.

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And into this weird, dark world came an equally weird American - called Colonel OIiver North. He was a radical Christian fundamentalist who wanted to save his, and Reagan's, global revolution through an audacious and, in retrospect, completely crazy plan.

North was high up in the National Security Council and had been running a secret programme to help the Contra guerrillas in Nicaragua - it was part of what he saw as an epic battle of good vs evil all around the world. But Congress had found out about it - and stopped him.

So in 1985 North, began to build an amazing scheme. He knew that the Iranians were desperate for weapons in their war against Saddam Hussein, so he proposed to sell them thousands of missiles, then take the Iranian money and use it to secretly fund the Contras. The Iranians would also persuade the Hezbollah guerrillas in Lebanon to release American hostages.

North, along with the National Security Adviser, Bud McFarlane, told Reagan that this would also be a way of opening a dialogue with "the moderates" in the Iranian regime. And out of this North built an epic vision whereby this would allow America to defeat the extremists in Iran, end the Iran-Iraq war, and root out all Islamist terrorist networks in Europe and around the world.

A journalist called Ann Wroe wrote a fantastic book in the 1980s about the Iran-Contra affair. What she describes is an incredible comedy - somebody should make a drama about it.

North gave everyone and everything code names:

Missiles were "dogs"

The airport was "a swimming pool"

Iran was "apple" - so Tehran airport was "apple swimming pool"

But confusingly in another code sheet Iran was "tango"

Israel was "banana"

The United States was "orange"

Hostages were "zebras"

So a typical message in North's notebook was:

"IF THESE CONDITIONS ARE ACCEPTABLE TO THE BANANA, THEN ORANGES ARE READY TO PROCEED"

But it got more confusing because North kept on giving himself different code names. Initially he called himself "Wagner", but then he began sending messages about the plan signed "Steelhammer". Then he called himself "Colonel Goode", while his right hand man, General Secord was codenamed "General Kopp". And then he started calling himself "Mr Green".

Here are two orange zebras:

At times North got confused about who he was. When he boarded planes he couldn't remember what name he was on the passenger list - and had to go through all of them until he got it right.

North and McFarlane started meeting with representatives of the Iranian regime in great secret in places like Frankfurt. They were convinced they were dealing with "moderates", but no one could define what a moderate was in Iran - especially when it began to seem that "conservatives" in the theocratic regime were also "radicals".

The Iranians got thousands of missiles - and three hostages were released. But then Hezbollah kidnapped three more hostages - and the Americans were back at zero again.

But North was convinced that it would work because it was the meeting of two groups - from America and Iran - who both devoutly believed that their political aims had a grander, religious purpose. He flew to Tehran to try and solve it. North sat listening to his Iranian contact talking emotionally about Martyrdom. North replied

"Because I am a Christian, I understand and believe that when one dies in faith he will spend eternity in a far better place"

The Iranians got lots more missiles, North got more money for the Contras - but no more hostages released. He got desperate and arranged another meeting with the Iranians in Frankfurt. North took a bible with him in which he had persuaded President to write an inscription - and he gave it to the Iranians saying:

''We inside our Government had an enormous debate, a very angry debate inside our Government over whether or not my President should authorize me to say 'We accept the Islamic Revolution of Iran as a fact. He (the President) went off and prayed about what the answer should be and he came back with that passage I gave you that he wrote in front of the Bible I give you.

And he said to me, 'This is a promise that God gave to Abraham. Who am I to say that we should not do this?' ''

At one of their meetings, an Iranian came up to North's right-hand man, General Secord, and said:

"What's with this guy North? We just left a country full of mullahs, and what do I find here but another goddam mullah."

Then - at the end of 1986 - North's mad scheme was exposed. There was an enormous political scandal that nearly brought Reagan down. And the revolutionary visions of the religious right were finished.

The Iranians made great play of how mad Oliver North was. The then speaker of the Iranian parliament, Rafsanjani, held up North's bible for the world to see:

But the religious right in America didn't go away, instead - just like in Khomeini's Iran - it has mutated since the late 1980s into a rigid moral police force that has become an iron cage that possesses American politics and stops it progressing.

And that is what someone like Rick Santorum is. He's no revolutionary. He's just a conservative. But whatever happens to his campaign, the religious right is an active force in American politics. In particular they are among the keenest to bomb Iran.

Meanwhile in Iran there are parliamentary elections - but it's a contest between different factions of conservative religious fundamentalists, with the opposition excluded.

Forty years ago, in both America and Iran, religion was brought into politics as a revolutionary force - fuelled by a vision that it could be used to transform the world. But now, in both countries, that power has mutated into a backward-looking and hysterical conservatism that is doing its best to remove both countries from the dynamic force of history.

And look what happened in 1987 to one of the great leaders of that revolution in America - Jimmy Swaggart. But even when he faced his downfall, he was a great performer.