Not for the first time, the world finds itself in an age of great movements of peoples. And once again, the United States is confronted with the challenge of absorbing large numbers of newcomers. There are approximately 200 million migrants and refugees worldwide, triple the number estimated by the UN only seventeen years ago. In the United States alone, about a million new immigrants have entered every year since 1990, bringing the total immigrant population to more than 35 million, the largest number in the nation’s history. Though Americans take justifiable pride in our history as a “nation of immigrants,” the challenges are more complex than those the nation previously surmounted. For sending and receiving countries alike, this is a time of exceptional stress”and yet, a moment that offers opportunities as well.

All too often, these challenges and opportunities are discussed in narrowly economic terms, but an adequate understanding of today’s migration patterns would also have to include their relation to the approaching “demographic winter” in the affluent societies of Europe and North America. Despite what population-control advocates had predicted in the 1960s and 1970s, the chief demographic problem facing most countries today is not overpopulation but its opposite. All over the world, even in developing countries, populations are aging. In the wealthier nations, where the process is most advanced, declining birth rates and increased longevity mean that our populations now include a much smaller proportion of children and a much larger proportion of disabled and elderly persons than ever before.

The combination of low birth rates and greater longevity is already bringing the health-care and social-security programs of welfare states into crisis. Social-welfare systems were constructed in the late nineteenth and early twentieth centuries on the basis of a proportion of nine, or in some cases, seven active workers for every pensioner. Now Europe is approaching three workers per retiree, and those retirees are living much longer. (When those who created the first social-security systems chose sixty-five as the age of eligibility, they were counting on the fact that relatively few people would live beyond that age to become burdens on the state.) With increased longevity has also come increased need for medical care, which has become vastly more expensive than anyone dreamed when public health-care systems were first established.

Although Europe will experience the crunch first, the United States will not be far behind. Our 78.2 million baby boomers are fast approaching retirement age. Over the next twenty-five years, the age structure of the whole country will come to resemble that of “retirement states” like Florida, where a fifth of the population is already over sixty-five. President Bush stressed the urgency of the situation in his 2006 State of the Union Address, warning that “the retirement of the baby-boom generation will put unprecedented strains on the federal government. By 2030, spending for Social Security, Medicare, and Medicaid alone will be almost 60 percent of the entire federal budget. And that will present future Congresses with impossible choices”staggering tax increases, immense deficits, or deep cuts in every category of spending.”

Although awareness of this impending demographic storm is beginning to sink in, policymakers in Europe and the United States tend to frame it only as a “welfare crisis.” The falling birth rates that are fueling the welfare crisis, however, are symptomatic of a deeper crisis in beliefs and attitudes”a crisis involving changes in the meanings and values that people attribute to aging and mortality, sex and procreation, marriage, gender, parenthood, relations among the generations, and life itself. That deeper crisis is part of the fallout from what Francis Fukuyama called “The Great Disruption,” the revolution in behavior and ideas that came on us so suddenly in the late twentieth century that it was unforeseen by any demographer. Beginning in the mid-1960s, and over a mere twenty years, major demographic indicators in the United States and northern Europe rose or fell by a magnitude of 50 percent or more. Birth rates and marriage rates tumbled, while divorce rates, cohabitation rates, and births outside marriage climbed sharply.

Those same years, to be sure, saw impressive advances for many women and members of minority groups. But not all the innovations represented progress. Some tended to undermine the cultural foundations on which free, just, and egalitarian societies depend. For example, the notion gained wide acceptance that behavior in the highly personal areas of sex and marriage is of no concern to anyone other than the “consenting adults” involved. With the passage of time, however, it has become obvious that the actions of private individuals in the aggregate exert a profound influence on other individuals and on society as a whole. In fact, when enough individuals behave primarily with regard to their own self-fulfillment, the entire culture is transformed. Affluent Western nations have been engaged in a massive social experiment”an experiment that brought new opportunities and liberties to many adults but that has put mothers, children, and dependents generally at considerable risk.

The family breakdown has had ripple effects on all the social structures that traditionally depended on families for their support and that in turn served as resources for families in times of stress from schools, neighborhoods, and religious groups to local governments and workplace associations. The law has changed rapidly too, becoming less an element of stability and more of an arena for struggles among competing ideas about individual liberty, equality between men and women, human sexuality, marriage, and family life.

Now that the dependent population in affluent countries includes a much smaller proportion of children than ever before, increased pressure on social resources is already provoking generational conflict in the ambitious welfare states of northern Europe. If political deliberation about the impending welfare crisis remains within a framework based primarily on the idea of competition for scarce resources, the outlook for the most vulnerable members of society is grim”as witness the growing normalization of the extermination of persons who become inconvenient and burdensome to maintain at life’s frail beginnings and endings.

Opinion leaders in the aging societies of Europe and the United States have generally avoided mentioning the relation between the birth dearth and the need for immigration. Consequently, there has been little discussion of what should be obvious: An affluent society that, for whatever reason, does not welcome babies is going to have to learn to welcome immigrants if it hopes to maintain its economic vigor and its commitments to the health and welfare of its population. The issue is not who will do jobs that Americans don’t want. The issue is who will fill the ranks of a labor force that the retiring generation failed to replenish.

Meeting the challenge of the declining ratio between active workers and retirees will require many sorts of adaptations, but replacement migration will have to play a part in crafting effective responses. The good news is that America enjoys several advantages over Europe. To begin with, the United States has a fertility rate of 2.08 babies per woman, while in the European Union the estimated 2005 fertility rate was 1.47, well below the replacement figure of 2.1. More, the United States has a long history of successful experience in absorbing large numbers of new citizens from many parts of the world. (While the absolute number of new immigrants is currently the highest in United States history, it is proportionately less than in previous eras of large-scale immigration.)

A third advantage worth mentioning is that, while there is enormous diversity among the inhabitants of the American hemisphere, most migrants to the United States share certain important beliefs with most of the country’s present inhabitants. Not least of these, in the case of Latin America, are religious in nature. According to a 2005 poll of the United States and nine of its closest allies where people were asked how important a role religion plays in their lives, Mexico and the United States came out on top, with 86 percent of Mexican and 84 percent of American respondents saying religion was important to them. European countries, by contrast, are understandably anxious about what will happen to the functioning of their democracies if sizeable groups of immigrants do not come to embrace the core concepts in which those regimes are grounded.

So why isn’t the United States glad about Latin American immigration? Part of the answer is the economic cost of large-scale immigration. American wage earners often fear that migrants will drive down wages and take the jobs that remain. This fear is sometimes exaggerated, but it is not unfounded: The consensus among labor economists is that immigration has somewhat reduced the earnings of less-educated, low-wage workers. Many Americans are also concerned about the costs that illegal immigration imposes on taxpayers, with its strain on schools and social services, particularly in the border states. The desire to protect the national security of the United States, especially after the trauma of September 11, has played a role as well.

There are also some in the United States who want to close the door to newcomers simply because they are outsiders. Over the course of the twentieth century, that attitude seemed to be fading away, but in recent years sleeping nativist sentiments have been irresponsibly inflamed by anti-immigration groups. A few years ago, I wrote of the financial and ideological connections among extremist anti-immigration groups, radical environmentalists, and aggressive population controllers. What unites that loose coalition in what I called an “iron triangle of exclusion” is their common conviction that border controls and abortion are major defenses against an expanding, threatening, welfare-consuming, and nonwhite underclass. (I never suspected when I wrote those lines that they would cost me a half-year’s salary. But on the basis of a promised grant from a foundation whose causes included environmental protection, I had taken an unpaid leave from Harvard. Shortly after my article was published, the foundation reneged on its promise. It turned out that their idea of protecting the environment included keeping out immigrants and keeping poor people from having children.)

Good-faith anxieties about large-scale immigration are sometimes expressed in terms of social costs, such as a feared deleterious effect on the nation’s cultural cohesion or the stability of local communities. One would like to take comfort from the fact that similar concerns were expressed at the time of the great migrations of a century ago. Though marked by conflict and competition, the story of those earlier immigrants is, to a great extent, a story of successful integration.

But American culture in those days was characterized by a broader set of common understandings. The picture is more complicated today, with large-scale immigration taking place at a time when it is harder to specify, and therefore harder for a newcomer to discern, a widely shared view of what it means to be American.

To make matters worse, the community structures and religious groups that once played crucial roles in integrating immigrants have themselves been weakened. The old Democratic-party political machines that once brought new citizens into the political process at the local level have vanished. In their place, a new immigrant today encounters political institutions that were developed in response to the black civil-rights movement of the 1960s. The newcomer from Mexico, Brazil, or El Salvador becomes a generic “Latino” in preparation for initiation into the game of divisive racial minority politics.

Overshadowing all other concerns is alarm over the fact that there are 11 or 12 million immigrants in the United States who have entered or remained in the country illegally. To comprehend the depth of feeling attached to that issue, one has to keep in mind that there is no country on Earth where legal values play a more prominent role in the nation’s conception of itself than the United States. That was one of the first things Tocqueville noticed in his travels here in the early 1830s, and, as the country has grown larger and more diverse, its reliance on legal values has become ever more salient. In the culture struggles of the late twentieth century, Americans had to rely more heavily than ever on the Declaration of Independence, the Constitution, and the rule of law to serve as unifying forces. Persons who come from societies bound together by shared history, stories, songs, and images can easily overlook or underrate the importance of this aspect of United States culture. Persons who come from societies where formal law is associated with colonialism may well find the United States’ emphasis on legality rather strange. But no solution to the challenges of immigration is likely to succeed without taking it into account.

If the United States is to develop realistic, wise, and humane immigration policies, it will need a much fuller and better-informed public discussion. At present, the public debate is too often dominated by immigration alarmists who tend to ignore both our need for replacement migration and the human situations of the men and women who seek opportunities in the United States. Meanwhile, pro-immigration advocates show insufficient attentiveness to the legitimate concerns of citizens, while some others seem to want the economic benefits of migrant labor while turning a blind eye to the toll that the present situation takes on migrants and their families.

In the current atmosphere, it is extremely difficult to sort out the legitimate concerns from the sinister ones. There is thus an urgent need to increase public awareness both of the case for migration and of the likely social costs (both to migrants and the host country) when large-scale migration is not accompanied by well-thought-out strategies for integrating migrant families into the life of the communities where they settle.

To devise effective strategies, it will be necessary to forthrightly confront the issue of legality. As political scientist Peter Skerry has pointed out, “The debate over immigration has been locked into a compelling but misleading framework that distinguishes sharply between legal and illegal immigration. It has been all but impossible to resist the prevailing paradigm which assigns all negative outcomes associated with immigration to illegal immigrants, and all benign or positive outcomes to legal immigrants. But the social-order effects of immigration do not easily fit into this neat legal-illegal paradigm.”

Nevertheless, given the importance of the rule of law to most Americans, solutions will have to be found that avoid the appearance of rewarding law-breakers, yet shift the focus in individual cases to how the immigrants have comported themselves while in residence here. Proposals that draw on the time-honored concept of rehabilitation after paying one’s debt to society seem to point toward a path between amnesty and punitiveness.

We will need to focus especially on the education of immigrant children, for schools are the first sustained point of contact with a new culture. Yet, that path is filled with pitfalls, for, as any parent can testify, integration into contemporary youth culture can pose problems of its own. If the United States is to rise to all these challenges, governments at all levels will have to rely heavily on local communities and organizations, including the faith-based organizations that have played such important roles in easing the transition of migrants in the past, even though these institutions are weaker today than they were in former times.

With migration inevitable, the only question worth asking seems to be: How can the process be influenced so as to maximize the potential advantages and minimize the disadvantages for all concerned? With so much at stake for the United States and Latin America, conditions ought to be favorable for intergovernmental negotiations of the sort begun by the Mexican and U.S. governments in 2001. Those negotiations received a severe setback with the attacks of September 11, 2001. But the difficulties should not be permitted to obscure the many opportunities for cooperation based on the principle of shared responsibility for a shared problem. An honest and complete discussion of the legitimate concerns and objectives of the nations involved could highlight areas where our interests coincide, clarify areas of conflict, and lead to improved understanding of the options each country can reasonably be expected to consider.

The five principles set forth in the 2003 Joint Pastoral Letter issued by the Mexican and U.S. bishops, Strangers No Longer: Together on the Journey of Hope , might be helpful in setting the stage for new approaches that could expand the pie for both sending and receiving countries. The letter asserts that (1) persons have the right to find opportunities in their homeland; (2) when opportunities are not available at home, persons have the right to migrate to find work to support themselves and their families; (3) sovereign nations have the right to control their boundaries, but economically stronger nations have a stronger obligation to accommodate migration flows; (4) refugees and asylum seekers fleeing wars and persecutions should be protected; and (5) the human dignity and rights of undocumented migrants should be respected.

To those five principles, a sixth should be added: a principle recognizing the need for a highly diverse, rule-of-law society to be careful about the messages it sends to persons who wish to become part of that society. And the bishops might have done well to note, as Pope John Paul II did in Solicitudo Rei Socialis , that solidarity imposes duties on the disadvantaged as well as the advantaged: “Those who are more influential, because they have a greater share of goods and common services, should feel responsible for the weaker and be ready to share with them all they possess. Those who are weaker, for their part, in the same spirit of solidarity should not adopt a purely passive attitude, or one that is destructive of the social fabric, but, while claiming their legitimate rights, should do what they can for the good of all.”

Evidently, those general principles are in tension with each other in certain ways. To move from the level of principle to specific programs and policies will require enormous dedication, intelligence, creativity, and goodwill on the part of all concerned. It will require realistic discussion of the human and economic costs and benefits. But one thing seems certain: Given America’s relative advantages in this age of great migrations, it would be a tragedy if the sending and receiving countries of our hemisphere did not join forces to explore how these advantages can be maximized in ways that are beneficial to all concerned. Whether we now live in countries of out-migration or in-migration, the choices we make now will determine what kind of societies we bring into being for those Americans, both of North and South, who come after us.

Mary Ann Glendon is Learned Hand Professor of Law at Harvard University. This essay draws on statistics and analysis by Marcelo M. Suárez-Orozco and Peter Skerry.

Articles by Mary Ann Glendon