They came in larger numbers than the Italians, Germans or Irish did, dwarfing past numbers of immigrants by a ratio of two to one. Swaths of the Southwest now look more like Mexico than the U.S. More people in Miami speak Spanish than English. And, in the past 10 years, Hispanic immigrants settled far beyond the obvious gateway states of California, Arizona, and Texas, posing vast existential questions of identity, demography, and acculturation for cities as far-flung as Portland, Oregon, and Tulsa, Oklahoma.

Nowhere is this clearer than in the Lehigh Valley, a post-industrial enclave in Eastern Pennsylvania. In just the past decade, the cities of Bethlehem and Allentown, as well as nearby Reading, saw their Hispanic populations explode. The new arrivals tend to keep to themselves, living among their own, speaking Spanish, and generally lending credence to the 2004 warning of Harvard political scientist Samuel Huntington: Hispanic immigration will "divide the United States into two peoples, two cultures, and two languages," he wrote.

But in 60 or 70 or 85 years, few in the Lehigh Valley will remember fear-mongers like Huntington. Even the grandchildren of bodega-owners and Dominican hairdressers might forget, reminded only by family stories like my Aunt Mae's.

"Three generations," declares James Smith, an immigration researcher at the RAND Corporation. "By the time you get to the third generation, you can't distinguish between Americans and Hispanic immigrants. That's how long it takes to look like an American."

A bit of context proves useful here. In its 235-year history, the United States cycled through two distinct waves of immigration, and now stands in the midst of a third. The first, from 1840 to 1889, gave us things like Christmas trees and St. Patrick's Day parades. The second wave, which my aunt belonged to, ran from roughly 1890 to the start of the First World War. During that time, a whopping 3.7 million Italians, most of them poor, Catholic, and otherwise undesirable, washed up in East Coast ports. Huddled masses of Austria-Hungarians, Russians, and Poles followed in comparable numbers.

Because the population of the U.S. was markedly smaller at that time, each second- and third-wave immigrant had a proportionally larger impact on mainstream culture than each immigrant does today. At the height of the second wave, there were 8.8 incoming immigrants for every 1,000 Americans. Now the rate looks more like 4.6 per every 1,000.

The sudden influx of foreigners startled settled Americans, says Garrett Epps, a professor of constitutional law who has studied historical immigration. In the late 19th- and early 20th-centuries, Americans felt the same sense of suspicion toward Irish, German, and Italian immigrants that some feel toward Hispanics today. All three groups deviated from what Huntington identifies as the core "American creed," the set of values that defined traditional American culture. Among them: Christian religious commitment, individualism, and the "duty to try to create a heaven on earth," carried over by the pilgrims and their black-smocked ilk.