Today, such attacks have given way to a kinder, gentler campaign to promote marriage, with billboards declaring that “Marriage Works” and books making “the case for marriage.” These campaigns share the idea that people are willfully refusing to recognize the value of traditional families, and that their behavior will change if we can just enlighten them.

But recent changes in marriage are part of a worldwide upheaval in family life that has transformed the way people conduct their personal lives as thoroughly and permanently as the Industrial Revolution transformed their working lives 200 years ago. Marriage is no longer the main way in which societies regulate sexuality and parenting, or organize the division of labor between men and women. And although some people hope to turn back the tide by promoting traditional values, making divorce harder or outlawing gay marriage, they are having to confront a startling irony: The very factors that have made marriage more satisfying in modern times have also made it more optional.

The origins of modern marital instability lie largely in the triumph of what many people believe to be marriage’s traditional role: providing love, intimacy, fidelity and mutual fulfillment. The truth is that for centuries, marriage was stable precisely because it was not expected to provide such benefits. As soon as love became the driving force behind marriage, people began to demand the right to remain single if they had not found love or to divorce if they fell out of love.

Such demands were raised as early as the 1790s, which prompted conservatives to predict that love would be the death of marriage. For the next 150 years, the inherently destabilizing effects of the love revolution were checked by women’s economic dependence on men, unreliable birth control, harsh legal treatment of illicit children and their mothers’ social ostracism.

These restraints collapsed between 1960 and 1980. Divorce rates had long been rising in Western Europe and the United States, and although they leveled off following World War II, they climbed at an unprecedented rate in the 1970s. This led some to believe the introduction of no-fault divorce laws, which meant married couples could divorce if they simply fell out of love, had caused the erosion of marriage.

The so-called divorce revolution, however, is just one aspect of the worldwide transformation of marriage. In places where divorce and unwed motherhood are severely stigmatized, the retreat from marriage simply takes another form. In Japan and Italy, for example, women are far more likely to remain single than women in the United States. In Thailand, unmarried women now compete for the title of “Miss Spinster Thailand.” Singapore’s strait-laced government has resorted to sponsoring singles nights in an attempt to raise marriage rates and reverse the birth strike by women.

U.S. and British divorce rates fell slightly during the 1990s, but the incidence of cohabitation and unmarried child-raising continues to rise, as does the percentage of singles.

Both trends reduce the social significance of marriage in the economy and culture. The norms that traditionally penalized unwed mothers and their children have weakened or been overturned, ending centuries of injustice but further reducing marriage’s role in determining the course of people’s lives. Today, 40 percent of cohabiting couples in the United States have children in the household, almost as high a proportion as the 45 percent of married couples who have kids, according to the 2000 Census. We don’t have a TV show about that yet, but it’s just a matter of time.

By the 1970s, women in America and most of Europe could support themselves if they needed to. The 1980s saw an international increase in unmarried mothers (paving the way for Murphy Brown), as more people gained the ability to say no to shotgun marriages, and humanitarian reforms lowered the penalties for out-of-wedlock births. That decade also saw a big increase in cohabitation before marriage.

Almost everywhere, women’s greater participation in education has raised the marriage age and the incidence of non-marriage. Even in places where women’s lives are still largely organized through marriage, fertility rates have been cut in half and more wives and mothers work outside the home.

Countries are having to codify the legal rights and obligations of single individuals and unmarried couples raising children, including same-sex couples. Canada and the Netherlands have joined Scandinavia in legalizing same-sex marriage, and such bastions of tradition as Taiwan and Spain are considering following suit.

None of this means that marriage is dead. Indeed, most people have a higher regard for the marital relationship today than when marriage was practically mandatory. Marriage as a private relationship between two individuals is taken more seriously and comes with higher emotional expectations than ever.

But marriage exerts less power over people’s lives now that most Americans spend half their adult lives outside marriage and almost half of all kids spend part of their childhood in a household that does not include their two married biological parents. And marriage no longer determines political and economic rights.

It’s hard to believe we could revive the primacy of marriage by promoting traditional values. People may revere marriage in the abstract, but most have adjusted to a different reality. The late Pope John Paul II was enormously respected for his teaching about sex and marriage. Yet during his tenure, premarital sex, contraception use and divorce rose in almost all countries. The Bible Belt has the United States’ highest divorce rate. And although many American teens pledged abstinence during the 1990s, 88 percent broke that pledge, according to the National Longitudinal Study of Adolescent Youth released in March.

Although many Americans bemoan the easy accessibility of divorce, few are willing to waive their personal rights. In states where “covenant” marriage laws allow people to sign away their right to a no-fault divorce, fewer than 3 percent of couples choose that option. Divorce rates climbed by the same percentage in states that did not allow no-fault divorce as in states that did. By 2000, Belgium, which had not yet adopted no-fault divorce, had the highest divorce rates in Europe outside of Finland and Sweden.

Nor does a solution lie in preaching the benefits of marriage to impoverished couples or outlawing unconventional partnerships. A poor single mother often has good reason not to marry her child’s father, and poor couples who wed have more than twice the divorce risk of more affluent partners in the United States. Banning same-sex marriage would not undo the existence of alternatives to traditional marriage. Five million children are being raised by gay and lesbian couples in this country. Judges everywhere must apply many principles of marriage law to those families.

We may personally like or dislike these changes. We may wish to keep some and get rid of others. But there is a certain inevitability to almost all of them.

Marriage is no longer the institution where people are initiated into sex. It no longer determines the work men and women do on the job or at home, regulates who has children and who doesn’t, or coordinates caregiving for the ill or aged. For better or worse, marriage has been displaced from its pivotal position in personal and social life, and will not regain it short of a Taliban-like counterrevolution.

Forget the fantasy of solving the challenges of modern personal life by re-institutionalizing marriage. In today’s climate of choice, many people’s choices do not involve marriage. We must recognize that there are healthy as well as unhealthy ways to be single or to be divorced, just as there are healthy and unhealthy ways to be married. We cannot afford to construct our social policies, our advice to our own children and even our own emotional expectations around the illusion that all commitments, sexual activities and caregiving will take place in a traditional marriage. That series has been canceled.