When her husband was deported to Juarez in 2012, Amy Rios couldn’t just leave her Wisconsin life behind to join him.

In her hometown of Waukesha, Rios had a 2-year-old daughter to care for, an extended family network and a new career as a phlebotomist to maintain. It took nearly three years for Rios to reunite her family below the border in San José del Cabo, where her husband had found a job and a home.

“I have a big family back home that I was really sad to leave, but I was overall pretty excited to be back with my husband and have my family back together again,” she said.

For decades, immigration between the United States and Mexico was a one-way street. But while Amy and Luis’ path to Mexico was in some ways circumstantial, more and more Mexican immigrants in America are moving back to Mexico of their own volition. Mexico’s strengthening economy, bolstered by its unique status for trade through deals like the North American Free Trade Agreement (NAFTA), helped flatten the wave of immigration to the United States.

Yet President Donald Trump’s ambiguous proposals to renegotiate NAFTA – which he’s repeatedly described as “unfair” – and implement “border adjustment” taxes have threatened Mexico’s trade relationship with the U.S. and raised the possibility of restoring the high immigration levels of the mid-2000s.

“A strong Mexican economy makes the U.S. a safer country and makes the U.S. a more competitive country,” said Hector Romero, CEO of Signum Research. “Only people with very narrow views, now in the 21st century, see international trade as a zero-sum game.”

NAFTA, which began as the Canada-United States Free Trade Agreement and absorbed Mexico in 1994, dissolved virtually all of the existing tariffs and trade barriers between the three countries.

While the deal immediately opened up new opportunities for trade, it initially did nothing to quell the exponential rise in Mexican immigration to the United States that began more than two decades beforehand.

According to Pew Research Center, the number of Mexican-born immigrants in the U.S. more than doubled to 2.3 million between 1970 and 1980. It doubled again in each of the next two decades, growing to 9.4 million in 2000. At the height of immigration in 2007, 12.8 million Mexican-born immigrants were living in the United States, with the majority living in the country illegally.

In 1994, a period of political and economic turbulence in Mexico kept immigration levels rising. An armed rebellion and the assassination of a heavily-favored presidential candidate stoked fears of political instability, which sparked a financial crisis when the government waffled on a devaluation of the peso and drove many Mexicans to the United States.

In the early 2000s, other factors kept the wave of immigration churning. “Violence in Mexico escalated, and many Mexicans fled to the U.S. not because of the economic situation, but they tried to flee for security,” Romero said.

After the recession of 2008 destroyed 8.7 million American jobs and hobbled the economy, net Mexican immigration immediately began to stagnate and then decline. But according to demographers from the pro-immigration American Immigration Council, that the downward trajectory was also due to, among other variables, “strong economic growth and increasing job opportunities in Mexico.”

Romero credits NAFTA for much of that growth, especially in specific industries like textiles, automobiles and construction. “Different industries were able to boom because of NAFTA. And precisely because of that,” Romero said, “they don’t need to cross the border anymore.”

Mexico’s trade position has skyrocketed since NAFTA’s inception. As of 2016, Mexico is the seventh-largest producer of vehicles on the planet, with the U.S. as its biggest customer. Mexico’s textile exports have more than doubled since 1994 – up to $6.8 billion in 2015. And Mexican food exports have grown by more than tenfold to $10.7 billion in the same period.

A steadily increasing population and a weak economy led many Mexicans, like Luis Rios’s father, to look for work in America in the 1980s and ‘90s.

Rios, now 33, came to America with his mother and two sisters when he was 7 years old, and said he didn’t find out he was undocumented until his mid-twenties. At the time he was deported, he had been working in a Wisconsin children’s hospital as a certified medical interpreter, translating between non-English speaking patients and hospital staff.

Some economists are reluctant to link NAFTA with immigration. “A number of other things happened at the same as NAFTA,” said Darren Lubotsky, associate professor at the University of Illinois at Chicago. “So I don’t think we have a definitive answer to how much NAFTA contributed to migration from Mexico to the United States.”

President Donald Trump has called NAFTA “the worst trade deal maybe ever signed anywhere, but certainly ever signed in this country,” and vowed to grow the economy while keeping American companies from hiring overseas. He has also promised to crack down on illegal immigration from Mexico, in part through the construction of a wall along the entire U.S.-Mexico border.

But strengthening the U.S. economy while making it more difficult for Mexico to engage in free trade could reverse the downward trend in Mexican immigration.

“You don’t want Mexican labor. That’s fine. So you need a strong Mexican economy that can accommodate these millions of people who otherwise would, one way or another, cross the border,” Romero said. “They will. No wall will stop them.”

And Trump’s promise to “buy American and hire American” could disincentivize Mexicans in the U.S. from following the lead of the Rios family and returning to their home country.

Now together in San José del Cabo, the Rios’s say they’re thriving in Mexico. Luis is working from home as a medical interpreter to American hospitals through a Mexico-based company. Amy is a virtual legal assistant, filling out forms and cover letters for a Seattle-based law firm.

“I feel like we have a better quality of life in Mexico than we did in the United States,” she said.

While Amy and Luis have considered returning to their Wisconsin families should the opportunity arise, they and their daughter, now 7 years old, are making the best of their time in Mexico as long as they can.

“We are very comfortable here,” Luis said. “It makes our decision hard.”