[Jon Meacham is the Editor of Newsweek. Meacham’s latest book, American Lion: Andrew Jackson in the White House, won the 2009 Pulitzer Prize for biography or autobiography...He has written for The New York Times Book Review, The Washington Post, The Los Angeles Times Book Review, and The Washington Post Book World...Meacham graduated from The McCallie School and from The University of the South in Sewanee, Tennessee, with a degree summa cum laude in English Literature.]

For years American conversation about Iraq has included a refrain about how we cannot expect to create a Jeffersonian democracy on the Euphrates. The admonition is true: if you think about it, America itself is not really a Jeffersonian democracy either (we are more of a Jacksonian one, which means there is a powerful central government with a cultural tilt toward states' rights). And yet Jefferson keeps coming to mind as the drama in Iran unfolds. The events there seem to be a chapter in the very Jeffersonian story of the death of theocracy, or rule by clerics, and the gradual separation of church and state. In one of the last letters of his life, in 1826, Jefferson said this of the Declaration of Independence: "May it be to the world what I believe it will be, (to some parts sooner, to others later, but finally to all,) the signal of arousing men to burst the chains, under which monkish ignorance and superstition had persuaded them to bind themselves."

However strong they may be for a time, theocracies cannot finally survive modernity, because one of the key features of modernity is the shift of emphasis from the privileges and power of institutions (a monarch, a clerical establishment, the state itself) to the rights and relative autonomy of the individual. In many ways, the modern virtues are the ones we associate with democracy: a free (or free-ish) flow of ideas, capital and people in an ethos in which men and women are free (or, again, free-ish) to form their own opinions and follow the dictates of their own consciences. By their very nature, theocracies are at risk in the face of such a world, for they are founded on an un-modern and undemocratic idea—that temporal power should be invested in those who claim that their decisions about the life of this world carry divine authority from a deity who dwells in the world to come.

To say that theocracies are doomed is not to argue that religion is any less important in our age. Quite the opposite: religious faith is an intrinsic element of human experience ("All men," said Homer, "have need of the gods"), and religion can be the undoing of a religious establishment, for an individual's interpretation of the applications of faith to politics may well differ from the institutional interpretation. There is a deep irony at work here. Theocracies usually mandate the teaching of religion, but the teaching of religion—the spread of texts and commentaries, the opening of theological debates among the people as well as the clerics—can lead not to uniform public belief but to a questioning of orthodoxy.

Which is always a favorite activity of a new generation. The products of one world often react against the world of their parents: the descendants of the established church in Colonial America, for example, grew up to favor religious freedom. In Iran, many of those protesting the regime have come of age after the 1979 revolution that brought Ayatollah Khomeini and his velayat-e faqih, or rule by the Supreme Jurist, to power....