It's long been inevitable: a 21st century North America of increasingly mixed peoples, the great rivers of Anglo and Hispanic population mixing and flowing freely along with Asian and African-American tributaries. Globalization, Internet-era communications and people yearning for opportunity all point to a time of melting of national borders, delayed only by anti-terrorism protections.

Still, history may well record May 1, the day hundred of thousands of legal and undocumented Hispanics and their allies turned out in the massive, unified pro-immigrant demonstrations across the continent, as a critical turning point.

Suddenly, a more human face was put on striving immigrants, perhaps ``illegal'' under law but quintessentially American in their personal aspirations. And direct support of already naturalized, voting Hispanics, America's fastest-growing voting bloc, was dramatized.

Also clear from May 1: how hopelessly out of tune with new reality the House of Representatives was with its immigration bill to hunt down and deport millions of today's illegal immigrants and to construct huge Berlin and Israeli-style walls along the Mexican border.

It's true, there are aspects to illegal immigration -- exploitive and violent coyotes, tunnels, death on the desert -- that we all abhor. Not to mention the disgraceful wages (plus zero benefits) some U.S. employers force on intimidated ``illegals.''

But a radically different picture emerges if one focuses instead on new people-to-people and cultural ties, the emerging economies and opportunity scenarios emerging along America's flank to Mexico and broader Latin America.

In San Antonio, one hears about ``mestizo,'' the idea of borderland regions ``fusing north and south'' in a new cultural synthesis in which ``differences are not destroyed, hidden or ignored.'' Our Citistates editorial team, preparing a series for the San Antonio Express-News, expected to find San Antonio's future defined by its ties to high-tech Austin just to the north. But instead, people focused on deep social and economic ties to Monterrey, Mexico, plus fast-rising NAFTA trade passing through border cities. There's a new trans-border culture, where hamburgers meet salsa and mariachi bands play at high school football games.

In a project in South Florida -- Miami-Dade County, Fort Lauderdale and Palm Beach -- we anticipated continued focus on the region's historic crops: tourists and housing for retirees. Instead, we found South Florida's brightest new frontiers in expanding trade ties to the Caribbean and Latin worlds, including film, Internet and broadcasting opportunities, as Miami exploits its position as de facto cultural capital of South America. And small wonder: with its polyglot of peoples, contentious, turbulent, creative Miami and its South Florida neighbors are like a ``dress rehearsal for America.''

Especially interesting ties emerged viewing the region we called ``the San Diego-Tijuana citistate.'' Its international boundary is one of the world's busiest, with more than 60 million northern passages each year, most for local shopping or recreation, but also many Mexicans entering the U.S. daily for jobs in San Diego.

It's true: immense numbers of illegal boundary crossers are apprehended at San Diego. Tijuana is troubled by rampant drug cartels, kidnappings and murders. Still, the Baja California standard of living has risen sharply -- today it's more a Second (rather than Third) World economy. And illegal passage at San Diego may not be the biggest border problem: because of delays (often up to two hours) at the border, about $4.2 billion in economic value (``the equivalent of seven Qualcomms," as some locals put it) are lost each year.

But the potential for economic growth and jobs is immense, reports San Diego Dialogue, the trailblazing binational citizen-business partnership begun in 1991. In its latest report, ``Borderless Innovation," the group points to big potentials in such clusters as biomedical devices, marine biotechnology, aerospace, defense and pharmaceuticals. Sophisticated skills are growing on the Mexican side, though the prevalent pattern remains research and development in San Diego universities and corporations matched by production in maquiladora plants on the Baja California side.

Now the San Diego Chamber of Commerce has a Mexican business center with a joint San Diego-Tijuana board. San Diego's new mayor, Jerry Sanders, took time out from the prickly pension crisis his city faces to confer with Tijuana leaders. Now he's scheduled to join a binational team, including San Diego business and civic leaders and the governor of Baja California, visiting Washington to impress federal officials on the border's economic importance.

Do these developments and trends mean U.S. immigration debates will ever be ``settled"? Likely not. But cross-border personal and economic ties are growing rapidly -- political analyst Steven Hill even projects increasing flows of American retirees emigrating to Mexico for warm climate and low costs.

Some Washington politicians may still be talking impregnable steel fences. But are walls the future? Or even if constructed, will they stem a convergence through this century of the two nations' economies and cultures? Not likely.

Neal Peirce's e-mail address is nrp@citistates.com