With the landscape and demographics of the United States evolving, the USA vs. Mexico rivalry has taken on different significance, writes Grant Wahl.

This story appeared in the October 12, 2015, issue of SPORTS ILLUSTRATED. You can subscribe to the magazine here.

The Brambilas—José and José Jr., of Ontario, California—take pride in their close relationship and the bonds they've built through their mutual love of soccer. But when the U.S. meets archrival Mexico in Saturday's CONCACAF Cup at a sold-out Rose Bowl in nearby Pasadena, theirs will be a house divided over the most fundamental of choices: Whose side are you on?

José Sr., a 55-year-old trucking company owner, will wear the green jersey of Mexico, like so many other Mexican-Americans who were born in the U.S. but grew up cheering for El Tri. But José Jr., a 21-year-old journalism student at University of La Verne (California), is part of an emerging demographic of second- and third-generation hyphenates. A die-hard fan of the Stars and Stripes, he has a U.S. Soccer tattoo on his right forearm and chose his Twitter handle (@Jozy_Brambila7) to honor forward Jozy Altidore.

"My dad teases me but not on the level of my mom's side of the family in Mexico," says José Jr. "They call me pocho"—a term for a person with Mexican roots who has embraced U.S. culture. "I tell them, 'I love Mexico as a country. And I love my family. But I feel 100% American.'"

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We hear a lot of talk these days about building a wall between the U.S. and Mexico, and it's no surprise that the loudest voice behind those calls—Republican presidential candidate Donald Trump—has been a fixture of the buildup to the 66th soccer match between these neighboring nations. The Mexican television channel TV Azteca went viral with a hype video for the game featuring Trump's voice laid over highlights of sad U.S. players. ("We don't have victories anymore. ... The American Dream is dead.")

Against the backdrop of the Build-a-Wall debate, though, this week's game can help remove barriers between the two countries and their respective sports cultures.

First, this game matters: It's arguably the most important U.S.-Mexico match since World Cup 2002, a showdown for regional supremacy and a berth in the '17 FIFA Confederations Cup—essentially a World Cup dry run—in Russia.

What's more, fans of each team have come to care in critical mass. Unlike previous U.S.-Mexico games at the Rose Bowl, in which Mexico fans filled 90% of the stadium, the crowd of over 90,000 Saturday is expected to be much more evenly balanced, more like 60–40 in Mexico's favor.

GALLERY: USA vs. Mexico through the years

USA vs. Mexico Soccer 19 Gallery 19 Images

That change is partly attributable to CONCACAF's allotment of large blocks of tickets to the U.S. and Mexican federations for distribution, but there are also simply more hardcore U.S. fans these days. Korey Donahoo, co-founder of the supporters group American Outlaws, says his organization nearly doubled in size around World Cup 2014, growing from 18,000 to 32,000 members in what are now 180 chapters (the latest: AO Anchorage). More than 4,000 AO members will travel to Pasadena from all over the U.S. Not to be outdone, Pancho Villa's Army, a U.S.-based supporters group for Mexico fans, will also be on hand with some 1,500 members.

If you're under age 35, it's unlikely that you've sensed any stigma attached to being a soccer fan in the U.S.; fútbol is cool these days. Breaking down the demographics by Facebook likes (a rough estimate), the American Outlaws are most popular among ages 25 to 34 (35%), 18 to 24 (26%) and 35 to 44 (19%). Anecdotally, at least, those young supporters include an increased number of U.S. fans such as José Brambila Jr.

Like most aspects of a hyphenate identity, however, national team fandom is a complex thing.

Kohjiro Kinno for Sports Illustrated

"Out of 10 personal [Mexican-American] friends, I'd say four are die-hard U.S. fans and the others are Mexico fans," says José Jr. "When the U.S. isn't playing Mexico, they support the U.S. because they were born here. But when Mexico plays the U.S., they feel like they're betraying their heritage if they cheer for the U.S."

Nobody is more aware of the gigantic stateside following for Mexican soccer (and the growing stature of the U.S. team among Spanish-speaking Americans) than Juan Carlos Rodríguez, president of Univision Deportes, which will air the U.S.-Mexico game in Spanish.

Rodríguez notes, "[The Mexican league] is by far the most-watched soccer league in the U.S. And the Mexican national team is the most-watched soccer team in America, regardless of language. It is the jewel of the crown.

"But the U.S. is everyone's team now too. For second- and third-generation Mexicans, it has become their No. 2 team at the very least. So you have a first-generation Mexican cheering for Mexico. And you have a second-generation Mexican struggling over whom to cheer for. There are going to be nearly 100,000 people [at the Rose Bowl on Saturday] and millions watching [on TV] cheering for both teams with a very nonpolitical mind-set."

In other words: removing barriers, dissolving walls.

That's not meant to be naive, of course. A soccer game won't erase the immigration debate, and one of the world's great rivalries will no doubt produce flash points on the field and in the stands.

How far they've come: State of USA vs. Mexico rivalry, 10 years ago

"There are so many issues extraneous to the game," says Rodolfo de la Garza, a Columbia professor who specializes in immigration issues, citing Trump, the ongoing drug war and decades of contentious U.S.-Mexican relations. "The U.S. has been Mexico's one real [non-soccer] enemy in its history. So the Mexicans have an added incentive: Beat the historical enemy, beat the insulting enemy and beat a good team."

Yet even then you can argue that soccer itself is helping to tear down walls. Until the 1990s this rivalry was so one-sided in Mexico's favor that nobody cared much on either side of the Rio Grande. Most telling of the ensuing reversal: The U.S. has beaten Mexico by a 2–0 score so often in the last 15 years that U.S. Soccer applied to trademark the phrase "dos-a-cero."

New chapters only add to the rivalry's rich history. Mexico's 4–2 victory in the 2011 Gold Cup final resulted in the firing of U.S. coach Bob Bradley. Two years later Mexico was seconds away from the indignity of being knocked out of World Cup 2014 during the regional qualifying tournament. Survival depended on charity from the U.S., which had already qualified, and there was Graham Zusi (San Zusi now south of the border) delivering a last-minute goal to knock out Panama and save Mexico's chorizo. "God Bless America!" screamed the TV Azteca commentator.

These days it's a major North American sporting event whenever the U.S. and El Tri take the field, and their countries fight to recruit dual-citizen players the way SEC schools might grapple over a prized tailback. This week's U.S. squad includes three members who could have chosen to play for Mexico (goalkeeper Nick Rimando and defenders Ventura Alvarado and Michael Orozco); Mexico's has one (goalkeeper Moisés Muñoz) who could have worn the Stars and Stripes.

The winner of this meeting gets a trophy and the Confed Cup berth—but there may be more at stake. In the 15 months since the U.S. reached the World Cup round of 16, coach Jurgen Klinsmann's crew has fallen into a funk, underscored by a fourth-place finish in the 2015 Gold Cup.

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Is Klinsmann's job in jeopardy? His boss, U.S. Soccer president Sunil Gulati, says Klinsmann will be safe even if the U.S. loses on Saturday.

But if that happens, you can be certain that for the first time during the coach's four-year tenure there will be widespread calls in the U.S. media for the German with the $3 million-plus annual salary to be axed.

If that sounds like the script for a telenovela, consider the drama on the other side. Mexico coach Miguel Herrera was fired just two days after his team won the Gold Cup in July. His offense: allegedly punching a Mexican media personality—the same TV commentator who cried "God Bless America!"

These latest plot twists have only increased the banter inside the Brambila household as the clock ticks down to Saturday's kickoff. But even then, all is not as simple as it seems. These days José Sr. coaches the youth soccer team of his 12-year-old daughter Isabel, who's a goalkeeper.

"My dad wears a Mexico jersey, but he loves the U.S. women's national team," says José Jr. "My sister is a huge Hope Solo fan, and her dream is to play for the U.S. So when it comes to women's soccer, he's a U.S. fan."

José Jr. laughs. So does his father. National team relationship status: It's complicated.