Conservative American columnist Daniel Pipes concludes a recent article for the New York Sun on Iranian president Mahmoud Ahmadinejad with the following words: "The most dangerous leaders in modern history are those… equipped with… a mystical belief in their own mission. That, combined with his expected nuclear arsenal, makes him an adversary who must be stopped, and urgently." As evidence of Ahmadinejad's mysticism Pipes cites the fact that he believes in Mahdaviat, the 'second coming' of the 'Mahdi', an Islamic version of the Messiah. Such radical religious beliefs, held by the leader of a powerful nuclear state, Pipes argues, will have ominous consequences. No doubt he is right. But if Pipes is concerned about the rise of powerful nuclear-armed men who believe in the second coming, he might have looked a little closer to home. Forget Iran. The mainstay of religious radicalism and mainstream occultism, is the United States, and America already has the bomb. More than one. Consider these statistics: 95 per cent of Americans believe in God; 86 per cent believe in Heaven; 78 per cent believe in life after death; 72 per cent believe in angels; 71 per cent believe in Hell; 65 per cent believe in the Devil; 34 per cent believe that the Bible is inerrant. But then again only 40 per cent believe they have actually had contact with the dead (source Kosmin and Lachman and The Economist).

America is a country where beliefs of this sort are commonplace. According to the National Survey of Religious Identification (NSRI) (whose estimates are more cautious than some) 20 per cent of the American population – 50 million people – can be called Evangelical Christians; that is, Fundamentalists. While Fundamentalist beliefs can appear extreme, in terms of numbers American Fundamentalism is not a fringe phenomenon.

Fundamentalism is a term more often used than understood, applied in a rather casual way to literalist followers of many religious texts. In relation to American Christianity, however, the term does have a clear historical origin. The word 'Fundamentalism' originally referred to a series of a dozen pamphlets entitled The Fundamentals which were distributed free of charge by the American Bible League between 1909 and 1915. The project was funded by two brothers, Lyman and Milton Stewart, who had made their fortunes in the California oil industry, and 250,000 were printed.

The Fundamentals emphasised two key points. The first was the truth of the infallible Bible, the conviction that the Old and New Testaments represent the complete and exact word of God and are the comprehensive and final authority over faith and practice. The second point stressed the concept of the 'born again' Christian, the insistence that salvation and eternal life come only as the free gift of God's grace through a radical and sudden commitment to Christ.

Fundamentalism has thrived in America since the end of the Second World War, usually under the name Evangelical Christianity, which is seen as less pejorative. The success of the movement since 1945 is due to a number of factors. The first is the general prosperity of the post-war years, for Fundamentalism is a faith of the economically comfortable, and in that it is similar to Calvinism in general. Secondly, there was a religious revival during the 1950s, when Fundamentalism successfully reflected the values of the times. Billy Graham, that era's most prominent preacher, described by George W Bush as 'America's pastor', dressed like a successful businessman and used television to convince viewers to make a 'decision for Christ'. He spoke the language of American individualism, emphasising personal sin and the benefits of coming to Christ. The third factor was the perceived threat of communism, which came to replace evolution as the chief satanic ideology in the Fundamentalist cosmology. It was an easy substitution: like evolution, communism came from abroad, it spread subversively and uncontrollably, and it undermined Christianity. Russia was seen as the headquarters of the Antichrist on Earth, and this political stance endeared Fundamentalists to American administrations, and anti-communist politicians to Fundamentalists, for many decades.

What are its core beliefs? Fundamentalism places a determined emphasis on the "realm of the unknown; the supernatural world or its influences, manifestations, etc," which is the definition of the word 'occult' in the Oxford English Dictionary. The occult tradition is a coherent intellectual stream that has roots in metaphysics, cosmology and religion and which has tried to bring together widely disparate aspects of God's Creation within a complex structure of connections, sympathies and affinities. Within its realm are numerous sub-systems such as magic, astrology, demonology, kabbalah, numerology, pyramidism, divination and theurgy. An occult quality is one which is hidden from the senses, as opposed to a manifest quality which is readily apprehended. As such it would come to include the more supernatural elements of religion, such as providence, prophecy and millenarianism. At the bottom of all this is the firm conviction that there is a plan to the universe, an underlying structure, and if only we understood it, not only would that knowledge make us happy, but we might even be able to manipulate its operation.

Specifically, Fundamentalists believe in the imminent, visible, sensible and dramatic Second Coming of Christ, according to a plan worked out from encoded references in the Bible, and with supernatural implications for everyone living today. Jesus himself, according to the Bible, spoke of his Second Coming, and gave a good many hints about the characteristics of the apocalypse, the revelation of Christ. In the 24th chapter of Matthew, Jesus reveals to his disciples that his return will be preceded by false prophets, wars and rumours of war, nation rising against nation, famine, plague, earthquakes, the darkening of the sun and moon, stars falling from heaven, and an undefined "sign of the Son of man in heaven". The abomination of desolation spoken of in Daniel 12:11 will be set up "in the holy place". Just when all hope is lost, "they shall see the Son of man coming in the clouds of heaven with power and great glory." A trumpet will sound, and angels will "gather together his elect from the four winds, from one end of heaven to the other."

The Revelation of St John the Divine gives further details. He speaks of a "beast" who rules over mankind for 42 months, is granted "great authority" by Satan, and is assisted by a second beast (later called the "false prophet"), gaining many followers by performing "great wonders". Terrible persecution follows for all who refuse to worship the Beast's image, and they are executed. In order to buy and sell, everyone has to receive a mark either in the right hand or on the forehead, consisting either of the Beast's name or his number, 666. (These bestial personalities will later fuse in popular lore with Satan and become the 'Antichrist'.)

At a certain point, the kings of the whole world gather at "a place called in the Hebrew tongue Armageddon" – Har Megiddo, the mountain of Megiddo – followed by natural disasters and ultimately the appearance of the Messiah on a white horse:

"His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself. And he was clothed with a vesture dipped in blood: and his name is called The Word of God. And the armies which were in heaven followed him upon white horses, clothed in fine linen, white and clean. And out of his mouth goeth a sharp sword, that with it he should smite the nations…. And he hath on his vesture and on his thigh a name written, KING OF KINGS, AND LORD OF LORDS."

The Beast and the False Prophet are defeated in battle, and cast "alive into a lake of fire burning with brimstone", with Satan thrown into a bottomless pit for a thousand years. It is during this millennium that Christ rules on earth with those "which had not worshipped the Beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years." This is the basis of the idea of a 1000-year rule by Christ and the saints.

The text notes that this glorious fate is not promised to everyone, "But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection." After the end of the thousand years, Satan is released for a final battle, again defeated, this time forever, to join the Beast and False Prophet in the lake of fire. Jesus only then sets up "a great white throne" for the Last Judgment of all human beings who ever lived, as "a new heaven and a new earth" descend from above "for the first heaven and the first earth were passed away."

All well and good, and backed by biblical authority of the highest kind. At the end of the 19th century, however, a new twist was added to the story, thanks particularly to Irish theologian John Nelson Darby (1800-82). His system was known as 'Dispensationalism', and today Evangelical Christians are almost invariably dispensationalist in theology. The term 'dispensation' refers to distinct eras of history, of which the End of Days is the seventh and final and seventh one, the others being Edenic, antediluvian, postdiluvian, patriarchal (Abraham to Exodus), legal (Exodus to Christ), and ecclesiastical (Christ until the final days).

Darby argued that Christ's kingdom is entirely future and supernatural, and that the divine plan can be worked out by paying careful attention to Daniel 9:24-7, in which a 70 week programme is described:

"Seventy weeks are determined upon thy people and upon thy holy city, to finish the transgression, and to make an end of sins, and to make reconciliation for iniquity, and to bring in everlasting righteousness, and to seal up the vision and prophecy, and to anoint the most Holy."

"Know therefore and understand," Daniel goes on, "that from the going forth of the commandment to restore and to build Jerusalem unto the Messiah the Prince, shall be seven weeks, and threescore and two weeks." Doing the maths, we add 7 + 60 + 2 and arrive at 69 weeks. The prophet Ezekiel taught us that in the Bible, each day stands for a year, so multiplying 69 x 7, we learn that there was a 483 year period between the rebuilding of the Temple during the days of Ezra and Nehemiah to the time of Jesus.

The last and 70th week, Darby argued, stands for the final seven year period before the Second Coming, so that the entire history of Christianity takes place in a suspended era between the 69th week and the 70th (last) week. The events of these final seven years will include the appearance of the False Prophet, who will lead the apostate churches, and the Beast, a political leader who will rule the 10 nations that grew out of the Roman Empire, as predicted in the simile of the 10 toes in Nebuchadnezzar's dream from the Book of Daniel. We will also see the return of the Jews to Palestine, the conversion of some of them to Christianity, the persecution of the other Jews, and the appearance of Christ to defeat the Beast, the False Prophet, and the renewed Roman Empire, in the great battle of Armageddon in the Holy Land. At this point, the thousand year rule of Christ on earth will begin: the millennium.

The last seven years of humankind will obviously be very trying. According to most dispensationalists, the saints of the true Church will be spared the tribulations of that time by being taken bodily out of the world in a process called 'the Rapture', returning with Christ after seven years. The textual reference for this procedure is 1 Thessalonians 4:16-17:

"For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord."

Modern Evangelical Christians take the Rapture very literally, and ponder the legal and practical difficulties of people suddenly disappearing from the Earth, vividly described in the Left Behind books, a series of religious thrillers which have sold tens of millions of copies.

In true modern occult fashion, Evangelical Christians have pondered the scientific process of the End of Days. Their imagination has been fired by the testimony in 2 Peter 3:10-12:

"But the day of the Lord will come as a thief in the night; in which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up. Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness, Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat?"

Quite obviously, argue Armageddon theologians, the reference here in the New Testament is to nuclear holocaust, which will be God's chosen method for destroying the old world, initiated by humankind itself.

Much has been written over the past few years about the increased role which Evangelical Christianity has played in the presidency of George W Bush. When reporter Bob Woodward asked the President if he consulted with his father about the war in Iraq, the younger Bush replied, "You know, he is the wrong father to appeal to in terms of strength. There is a higher father that I appeal to."

The popularity of this kind of decision-making process is not universal in the United States, so Bush often resorts to an esoteric code. This came out very forcefully, for example, in his address to the nation on 7 October 2001, only a month after 9/11, announcing air strikes against Afghanistan. He concluded his remarks with the curious phrase, "May God continue to bless America", the single word 'continue' transforming an anodyne cliché into a genuine religious sentiment.

Professor Bruce Lincoln of the University of Chicago submitted that speech to a line-by-line analysis, and found clear references to Isaiah, Job, and the Book of Revelation. The image of terrorists who "may burrow deeper into caves and other entrenched hiding places" sounds merely like awkward writing, Lincoln notes, yet it contains "biblical allusions plainly audible to portions of his audience who are attentive to such phrasing, but likely to go unheard by those without the requisite textual knowledge." This kind of Bible-talk enables George W Bush to communicate with initiates, winking at them conspiratorially as partners in a type of Christianity that is based on the careful reading of esoteric texts.

The Fundamentalist movement, a fusion of the occult tradition with popular Christianity, grew in strength throughout the twentieth century, and shows no sign of decline now. The sheer number of Fundamentalists has transformed religious extremism into part of American society's mainstream. The convergence between religious and political agendas in the Bush administration is also unprecedented. Contrasting Bush with previous presidents, communications analyst David Domke writes "Presidents since Franklin Roosevelt have spoken as petitioners of God, seeking blessing and guidance; this president positions himself as a prophet, issuing declarations of divine desires for the nation and world."

Facing off with other true believers in Iran just now might not be such a good idea, especially for the many millions of us who are unlikely to be raptured, and are less than eager to experience at close hand the seven years of tribulation.

David S. Katz is chair of the Department of History, Tel Aviv University and author of The Occult Tradition (Jonathan Cape)