By Jonathan Zimmerman

In the late 1840s, following a brief war with Mexico, the United States acquired the present-day states of California, Nevada, and Utah, along with parts of Colorado, Arizona, New Mexico, and Wyoming. Counting Texas, which was annexed before the war, about a third of the continental United States is former Mexican territory.

Should we celebrate or bemoan this? Was the Mexican War a victory for the "Empire of Liberty," as its advocates maintained, or did America prey on a weaker neighbor to advance its imperial designs?

Those aren't questions you'll hear in most public schools' U.S. history classes, which simply assume American righteousness. But you're also unlikely to hear them in "ethnic studies" classes, which often assume the opposite.

That's the subtext of the latest controversy in Arizona, which has become ground zero in America's continuing struggle to define itself. The combatants in this battle resemble each other much more than either side is willing to admit.

This month, Arizona adopted a law barring schools from teaching courses that "promote resentment toward a race or class of people" or "are designed primarily for pupils of a particular ethnic group." Promoted by state schools Superintendent Tom Horne, a GOP candidate for attorney general, the measure targets ethnic studies classes at four majority-Hispanic high schools in Tucson.

Critics around the country were quick to link the law to Arizona's notorious immigration measure, passed just weeks earlier, which gave police broad powers to detain suspected illegal aliens. Like the immigration law, they argue, the restriction on ethnic studies reflects racist whites' fear of Hispanics.

Nonsense, says Horne. "It's the opposite of racism," he told reporters. "We're trying to get schools to treat students as individuals and not on the basis of race." Indeed, the law prohibits courses that promote "ethnic solidarity" rather than treating pupils "as individuals."

But if Arizona schools really treated students as individuals, they would engage them in the controversies of the state's history - starting with the Mexican War. Contemporary critics of the war included Abraham Lincoln and Henry David Thoreau, who famously spent a night in jail to protest it. Would Superintendent Horne be at ease with a classroom debate on whether Lincoln and Thoreau were right?

I think not. If a mostly Hispanic classroom sided with the war's critics, it might violate Arizona's new ethnic studies law. Mexican American kids condemning U.S. imperialism? What could provoke more "resentment toward a race or class" than that?

By the same token, it's hard to imagine ethnic studies classes engaging in real debate along these lines, either. According to reports, some use Occupied America: A History of Chicanos, by the respected Mexican American historian Rodolfo Acuna, as their main textbook.

I like Acuna's book, but - like every historical account - it has a distinct perspective on the past. You can get a flavor of that perspective from the title of its chapter on the Mexican War: "Legacy of Hate: The Conquest of Mexico's Northwest." Section headings include "The Invasion of Mexico" and "The Myth of a Nonviolent Nation."

Do the ethnic studies classes in Tucson analyze the book's argument so students can decide if they agree? I doubt it. Like mainstream history classes, they probably present one point of view as the truth.

Ethnic studies defenders might say they're simply balancing out the ledger: Given the pro-U.S. propaganda Mexican American kids encounter in regular history courses, it's only appropriate that they hear the "other side" in ethnic studies classes.

Yet, by segregating critical perspectives in "ethnic" classes, we let the regular curriculum off the hook. Here in Philadelphia, for example, students must pass a course in "black history" to graduate. That makes it much easier for general American history classes to neglect the African American experience, which lies at the heart of the making - and the meaning - of America.

Worse, it denies kids the chance to make meaning on their own. If we give students one right answer in their regular courses and another in their ethnic ones, they'll simply parrot those answers back to us in each class. They won't have to puzzle out the truth for themselves.

So let's take the Arizona law at its word and treat all our students as individuals. That means exposing them, in all their courses, to the great diversity of people and ideas that make up America. And, most of all, it requires letting them make up their own minds - about America, Mexico, and everything else.