By Gregory Rodriguez (contributing editor to Opinion, is a senior fellow at New America Foundation).

After the collapse of the Soviet Union and the end of the Cold War, U.S. policymakers looked for new ways to understand America's place in the new world. What would be the primary focus of U.S. foreign policy? Who would be our greatest threats? Some academics, among them Harvard political scientist Samuel P. Huntington, feared that the absence of an "undesirable other" would weaken our national identity. The United States, Huntington contended, needed an enemy to serve as a foil "to promote identity and cohesion" among its people; nations, like individuals, define themselves in opposition to others.

Huntington's controversial thesis, known as the "clash of civilizations," helped fill the post-Cold War interpretive vacuum. Future international conflicts, he contended, would be drawn along cultural — rather than ideological, national or class — lines. The world's eight morally and politically incompatible civilizations, he predicted, would jockey for survival and influence. Though his Hobbesian vision was global in scope, some observers suspected that Huntington was actually projecting his anxiety over the future of the multiethnic United States onto the world stage. The true origins of Huntington's thesis, wrote Egyptian scholar Emad el-Din Aysha, "lie partly in problems Samuel Huntington sees brewing in his own country." Aysha was right.

This week, Huntington will publish the first excerpt of an explosive new book arguing, among other things, that continuing Latin American immigration could create a cultural clash between Hispanics and Anglos that would "replace the racial division between blacks and whites as the most serious cleavage in U.S. society." He warns that Mexicans, in particular, will increasingly refuse to assimilate into the mainstream and will create "an autonomous, culturally and linguistically distinct and economically self-reliant bloc" in the Southwest. The U.S., he says, would be divided into two peoples, two cultures and two languages.

Huntington has found the new enemy, and they are arriving from the south.

The argument is not the least bit new. In the mid-19th century, when the United States took control of the Southwest through conquest and annexation, some Anglo Americans feared that large numbers of unassimilable Mexicans would undermine national integrity. In 1847, South Carolina Sen. John C. Calhoun questioned whether the U.S. could "incorporate a people so dissimilar from us in every respect — so little qualified for free and popular government — without certain destruction to our political institutions?"

Nor is Huntington's attempt to define the U.S. in contradistinction to Mexico and Mexicans novel. During the mid-19th century conflicts with Mexico, Americans transformed the centuries-old belief in the superiority of Anglo-Saxon political institutions into a faith in the innate racial superiority of the Anglo-Saxon branch of the white race. Defining themselves in opposition to mixed-race Mexicans, a growing number of white Americans racialized Manifest Destiny. In 1836, Missouri Sen. Thomas Hart Benton claimed that the Texas revolution against Mexico "illustrated the Anglo-Saxon character, and [gave] it new titles to the respect and admiration of the world."

Huntington is no classic racist. If anything, he is a cultural determinist. It's not that he believes assimilation is impossible. Rather, he theorizes that the six factors that make Mexican immigration unique in U.S. history — proximity to homeland, size and persistence of migration, the problem of the undocumented, regional concentration and the historical presence of Mexicans in the Southwest — are combining to create a cultural climate in which immigrants and their descendants will refuse to assimilate and belligerently assert their ethnicity. His belief in cultural conflict leads him to treat cultural behaviors that are fluid and adaptable as if they were biologically predetermined. This tendency has led author and international-affairs columnist William Pfaff to call Huntington's clash thesis "a politically corrected version of what our grandparents called race war." In other words, Americans will struggle with Islam or Confucian civilization — and Mexicans — "because culture and religion make it so."

The problem with Huntington's theory is that it doesn't take into account the people whose actions it presumes to predict. In the more than a century and a half of Mexican American history, there has not been one serious, popularly supported movement to wrest control of the Southwest away from the U.S. or to isolate it from the rest of the nation. Nor have Mexican Americans ever shown much interest in distancing themselves from the mainstream by building parallel ethnic institutions.

For example, in Los Angeles, home to more Mexicans than any other city in the U.S., there is not one ethnic Mexican hospital, college, cemetery or broad-based charity. Ignoring Mexicans' history of racial and cultural blending and the reams of survey data that show Mexican Americans place great faith in U.S. institutions, Huntington resorts to sketchy, anecdotal evidence to prove the existence of Mexican American separatism. His examples of rowdy Mexican soccer fans hurling abuse on American players and a quote from a lunatic Chicano studies professor are also cited by Pat Buchanan in his book "The Death of the West." It never occurred to either man that this methodology is akin to gauging the sentiments of Anglo Americans by quoting white supremacist David Duke and citing the antics of Raider fans at the Oakland Coliseum.

As do many other contemporary scholars, Huntington overemphasizes both the influence of multiculturalism on immigrants and the coercive nature of assimilation. His theory suggests that Mexican Americans living in a majority-Hispanic region will have neither the desire nor the need to assimilate. He assumes that the presence of large numbers of Anglos is the sine qua non of assimilation. But places like south Texas have had majority-Hispanic populations for years, and separatism — political, cultural or economic — is nowhere to be found. Last week, Laredo, Texas, which has been overwhelmingly Hispanic since its founding in 1755, culminated its annual George Washington's birthday celebration, the largest in the nation. Lt. Gen. Ricardo Sanchez, the commander of allied occupation forces in Iraq, grew up in nearby Starr County, which is 98% Mexican American.

Still, the most troubling aspect of Huntington's thesis is its definition of assimilation. Like most Americans, he once believed that maintaining ethnic culture and traditions was "perfectly compatible" with sharing American political, social and economic values. Now he says it's not enough to believe in the American creed. "There is no Americano dream," he writes. "There is only the American dream created by an Anglo Protestant society."

Fearful of the world's encroachment on America, Huntington redefines the U.S. in the narrowest terms: If the U.S. is to cohere as a nation, immigrants must assimilate into Anglo Protestant culture. Ironically, Huntington's discovery of the new enemy will not promote the cohesion among Americans he sees as indispensable to the country's survival. On the contrary, it's the irrational fear of the "undesirable other" that has always been — and continues to be — the greatest threat to American national unity.