The U.S. isn’t the only place where Central American immigrants are seeking refuge.

The Trump administration has been focused on the country’s Southern border, most recently adopting a “zero tolerance” policy towards migrants that has changed the way people are treated as they seek asylum in the U.S. But the people trying to cross the border represent just a fraction of the people who are currently on the move in Central America, displaced from their homes in Mexico, Honduras, El Salvador and Guatemala by violence and poverty. Data on the movement of people in and out of northern Central America is imperfect, but its trend is clear: What’s happening at the U.S. border is part of a bigger, complex migration — and not all of it crosses borders.

There are likely hundreds of thousands of northern Central Americans who haven’t left their home country but have fled their homes. Rural, poor Guatemalans trying to escape drug traffickers and extreme poverty head to urban centers. El Salvadorans facing extortion and death threats from local gangs move to live with family in other cities or neighborhoods. “In the poorest sectors … people who are displaced move multiple times and then eventually might leave the country.” said David Cantor, director of the Refugee Law Initiative at the University of London. But the movement is also not limited to any one economic class, he said.

It’s hard to know just how many people are moving within borders, in part because many governments don’t acknowledge that internally displaced people exist at all. “The Government of Mexico does not officially recognize the phenomenon of internal displacement,” according to the Internal Displacement Monitoring Center, which tracks internal displacement and is based in Switzerland. When the center was founded in the 1990s, the international community was trying to figure out how to count and help the growing group of people impacted by war and violence who didn’t show up in official statistics because they weren’t crossing borders. For the past 20 years, IDMC has filled that role, collecting data on internally displaced people around the world.

It estimates that, despite the government’s lack of acknowledgement, 345,000 Mexicans were internally displaced by the end of 2017.

It’s also difficult to count internally displaced people in countries that do acknowledge them. In El Salvador, the most recent research conducted by the government suggests that about 1 percent of the population was displaced over the last 10 years, the equivalent of roughly 70,000 people. Based on its own research and qualitative analyses, however, IDMC (in addition to other researchers) believes the number is far higher. A national survey conducted by a local university found that 296,000 El Salvadorans were internally displaced in 2017 alone.

“Our two approaches are worlds apart,” said Justin Ginnetti, who leads the data collection for IDMC. Ginnetti says the El Salvadoran government’s data is based on random household sampling and an approach that’s meant to keep all parties happy, including a government fending off criticism from other political parties. “We don’t care about consensus; we care about accuracy.”

Understanding displacement is also difficult because there are multiple issues pushing people out of their homes. Cantor has studied how various kinds of violence, including street gangs, cartels and drug traffickers, affect displacement — it’s a complicated ecosystem. And because these aren’t discrete events like war or natural disasters it’s harder to connect the movement of people to the violence in Central America. Still, his research suggests a strong effect, particularly in places controlled by gangs.

There’s even less information available about the situations in Honduras and Guatemala, but IDMC’s research suggests that some 190,000 Hondurans and 242,000 Guatemalans were internally displaced in 2017. (Honduras has acknowledged its displaced population in recent years, establishing a commission on the subject. Guatemala has been less willing, according to multiple people who research the topic.)

Collectively, more than a million Central Americans have fled their homes without crossing a border, according to IDMC’s estimates.

“I think most Americans think everyone wants to come here and that is not the case,” said Elizabeth Ferris, a research professor at the Institute for the Study of International Migration at Georgetown University. “People love their countries and don’t want to leave.”

But in Central America, the safety issues often follow people when they try to move internally. And those fleeing violence there are increasingly likely to seek refuge in other countries of Central America. Though the vast majority of asylum seekers still make their way to the U.S., the number who have gone to Belize, Panama, Mexico and Costa Rica has grown as well, according to the United Nations Refugee Agency.

And even if they head to the U.S., they are increasingly likely to be stopped en route. Approximately 94,800 people from El Salvador, Guatemala and Honduras were apprehended crossing into the U.S. in 2017, but an additional 81,100 people from those three countries were stopped at the Mexico border.

In all, just a fraction of people fleeing violence and poverty in Central America each month is attempting to come to the U.S. And those who do make it to the U.S. have often moved internally before making the dangerous journey north, according to interviews by UNHCR and others.

The Trump administration’s recent policy shifts are supposed to deter only the fraction that make it to the U.S. border. It may work for a time, but policy changes at the border won’t improve the underlying causes of displacement in Central America. And other Trump administration policies combined with growing turmoil in Nicaragua could cause displacements to rise.

For example, many parts of Central America are reliant on money sent from family members in the U.S. When 250,000 Hondurans and El Salvadorans lose Temporary Protected Status over the next couple of years, it’s likely that some of that funding stream could dry up. It’s hard to predict how that will impact the country, but it’s easy to imagine local economies and resources for youth taking a hit, said Cantor, which could increase gang membership and violence. Economics and security are intrinsically linked in Central America, and both can push people to leave their homes.

Experts on refugees and migration are clear that closing the U.S. border won’t keep people from leaving their homes. Life-threatening violence and hunger are powerful forces; unless the underlying causes for displacement are addressed, people will continue to move somewhere.