Is the age of mass Mexican immigration to the United States about to end? In Shaping Our Nation, Michael Barone, one of the leading students of American demography and voting patterns, suggests that this might be the case. His contrarian take on Mexican immigration is part of a larger concern driving his fascinating and iconoclastic new book: Barone believes that both liberal and conservative commentators are too alarmist about the state of contemporary America, and he would like us all to relax.

Most Americans, consciously or unconsciously, use the post-World War II era as their baseline when analyzing the state of the nation. Conservatives may pine for an era of Ozzie and Harriet domesticity, but social scientists (mostly liberal) are in fact much more locked into the view that the United States from about 1945 to 1965 was "normal" and that any deviation from its standards represents an alarming deterioration in the conditions of American life. The '40s and '50s coincided with the social sciences' dramatic rise in American higher education, and the conditions observed then unavoidably influenced the assumptions and perceptions of later researchers in the field. For Barone, however, the relative stability of those postwar years was exceptional; for most of its history the United States has been a tumultuous, divided, and rapidly transitioning society marked more by conflict and competition among regions, classes, and ethnic and racial groups than by consensus and calm.

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Shaping Our Nation is the latest installment in a long project of investigation and reflection that has taken Barone from the first edition of his landmark Almanac of American Politics (1972) through books like Our Country: The Shaping of America from Roosevelt to Reagan (1990), The New Americans: How the Melting Pot Can Work (2001), Hard America, Soft America: Competition vs. Coddling and the Battle for the Nation's Future (2004), and Our First Revolution: The Remarkable British Upheaval that Inspired America's Founding Fathers (a 2007 study of Britain's Glorious Revolution in 1688). Through all these works, he has tried to understand the sources and nature of American society's dynamism. From this train of analysis comes a solidly grounded appreciation of the importance, and also the durability, of America's liberal, open society. In particular, he understands something that very few on either the Right or the Left grasp: that instability and turbulence are not a sign of pathology in American society; they are its natural condition, and an America that stayed tranquil and calm for very long would be in big trouble. This volume returns to a topic that has long fascinated him. American society is founded on the mass migration of peoples, and immigration has always been a prime source of the turbulence and creativity that undergird American wealth and power.

This is an opportune moment for such a book because immigration is one of the most polarizing questions in American politics, with advocates calling for legalization for millions of undocumented alien workers and families, while opponents call for measures to tighten border security and encourage illegals to "self-deport." The issue fuses questions of culture, identity, economics, and party politics: What kind of country do we—should we—live in? Who are the American people, and will immigration change our identity? What is the effect of immigration on income distribution? How will immigrants vote, and will new immigrants swell the ranks of what some call the "emerging Democratic majority"?

Shaping Our Nation will ruffle feathers on both the Left and the Right, but it offers insights that could change the way we think about an issue that isn't going away.

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First, Barone hammers home an important point: disruptive, uncomfortable, and challenging waves of immigration aren't some new and horrible phenomenon. From the 18th century, when waves of angry, anti-establishment Scots-Irish immigrants destabilized the cultural and political status quo of the seaboard colonial societies, right up to the present day, the United States has experienced successive mass movements of immigrants who vexed and changed the American order.

Second, he argues persuasively that waves of immigration from abroad are only one dimension of the story. Mass internal migration—from one part of the United States to another on an epic scale—has been equally disruptive and decisive in shaping this country. The (forced) migration of slaves from the old Atlantic seaboard tobacco and indigo plantations to the rich new cotton plantations from Georgia to Texas continues to shape the politics and culture of the South today. The huge migration of New Englanders into the Middle West and later into the Pacific Northwest created a transcontinental moral and political community still observable in present-day voting patterns. Twin movements of black and white workers from the South to new opportunities in the industrializing Middle West and (during and after World War II) in California, changed the face of urban and suburban America in ways we still struggle to understand and to cope with.

Third, Barone reminds us that every one of these waves, whether originating inside or outside the United States, caught contemporary observers by surprise. Each grew quickly and led observers to believe that it was going to continue—and accelerate—into the distant future. But each came to a sudden and unexpected end. In one case, the U.S. government was responsible, when restrictive legislation slashed immigration from much of central, eastern, and southern Europe after 1924. All the other waves of mass migration, internal and external, have started and stopped on their own, without any significant government intervention.

Barone's suggestion that large-scale Mexican immigration may be drawing to its close is based on this analysis. Numerically, he reports, the drop-off in Mexican immigration is comparable to the sudden decline in German and Irish newcomers in the 1890s. Although he acknowledges that it is too soon to be sure, he notes that since the economic downturn that began in 2007, both legal and illegal immigration from Mexico have fallen to much lower levels.

For many recent Mexican immigrants, the recession was particularly devastating. It struck hardest in states with large recent immigrant populations (like the "sand states" of New Mexico, Arizona, California, and Nevada), where the collapse of the construction industry destroyed many of their jobs. Beyond that, the housing bubble destroyed the savings of first-time homeowners, a group that included many immigrants. With the fertility rate in Mexico continuing to fall, and a combination of economic reforms and favorable international conditions leading to a revival of employment opportunities there, the peak of Mexican immigration to the U.S. may indeed have passed.

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Although Barone's approach is not partisan, it could be especially useful to Republicans, who are divided between libertarians endorsing open immigration and other conservatives taking a more skeptical view. The continuing desire of millions of people to seek opportunity here shows that the U.S. is still a beacon of hope around the world. As long as millions abroad think, "Yankee go home…and take me with you!" the American dream still holds its appeal. Moreover, one might think that many immigrants would lean Republican, attracted by a political platform that preaches growth and opportunity. Yet conservatives and immigrants aren't getting along well. Democrats conclude from this that the coming decades will be a time of lasting Democratic political hegemony; immigrants will be part of the "emerging Democratic majority" that analysts John Judis and Ruy Teixeira have predicted. Hispanic immigrants, despite some GOP success among Cuban-Americans (and likely success among Venezuelan immigrants escaping that country's implosion), have become steadily more Democratic in their voting patterns, with 62% voting for Al Gore in 2000 and 71% for Barack Obama in 2012. Asian-American immigrants, too: 31% voted Democratic in 1992, 73% in 2012.

These voting patterns should trouble GOP activists, but Barone's book points to another scenario. Social conservatives oppose immigration largely because they fear for the integrity of the Anglo-American cultural identity—the synthesis of old and new immigrants that the restriction laws of the 1920s tried to freeze in place. That old demography has been eroding since immigration was liberalized in the 1960s. Barone argues that the U.S. population's relative demographic stability in the 1950s was no more "normal" than other features of the post-1945 period in American life. The American character that social conservatives champion today is the product of centuries of demographic change, culture clashes, and political struggle. In fact, turbulence and change favor American dynamism, and social conservatives, he counsels, can and should view the changes taking place in America today with wary optimism rather than with bleak despair.

If Michael Barone is right that Mexican immigration has peaked and today's era of political polarization and cultural conflict represents a return to American norms rather than a dangerous lurch into unprecedented strife, Republicans may be able to reach out to immigrants with more confidence and less intraparty conflict. But whatever the political implications of this eminently clear and readable book, Shaping Our Nation affords every reader both a richer, better informed perspective on the forces that made America the country it is and a stronger appreciation of the continuing dynamism of American life.