CNN  — 

The images of thousands of Central American migrants packed onto a bridge at the Mexico-Guatemala border flashed across TV screens as leading experts on the region met last month.

For Andrew Selee and others gathered in El Salvador at an annual conference on Central America, the so-called caravan was a key topic of conversation.

“People were fascinated about how it had originated,” said Selee, president of the Washington-based nonpartisan Migration Policy Institute. “They were wondering, ‘Why now? Why are the caravans happening? Is this going to be the new thing out there?’ “

But Selee said one thing didn’t come up as they tried to sort out the situation: the US midterm elections.

“I was in three meetings on migration where the caravan was talked about. … Not one person mentioned that,” Selee said. “It’s just not on anyone’s mind.”

Tweets from President Donald Trump, a rash of conspiracy theories and rapidly escalating political rhetoric in the lead-up to a major vote north of the border aren’t what’s piquing experts’ interest in the large groups of migrants moving through Mexico.

But questions about what’s happening, why it’s happening and why it’s happening now are.

“We’re all trying to make sense of it,” Selee said.

Experts: US election has nothing to do with it

Experts say many factors are likely contributing to migrants’ decisions to leave Central American countries. But establishing exactly why more large groups appear to be forming now is more difficult to pinpoint.

“It’s hard to explain all this. It’s hard to figure out what the reason is,” Selee said.

But there’s one thing experts agree on.

“To see this as somehow timed one way or another to influence the US midterm elections is a mistake,” said Cynthia Arnson, director of the Latin America program at the Washington-based Woodrow Wilson International Center for Scholars.

“It is, without a doubt, having an impact on shaping the pre-election climate, and President Trump is making absolutely conscious and concerted efforts to inject this issue into the campaign, where he knows the Republican base cares deeply about it, but I see the timing as a coincidence.”

Mike Allison, a professor at the University of Scranton in Pennsylvania who studies Central America, also said looking at the formation of migrant groups through the lens of US elections is missing the point.

“This is simply the latest manifestation of a crisis that’s really affecting the entire Americas,” Allison said, citing drug trafficking, organized crime, corruption and the absence of democracy as underlying causes. Climate change also has started to fuel more migration, he said, as drier conditions in some areas have decimated crops.

‘A human tragedy’

Crowds started gathering outside a bus station in San Pedro Sula, Honduras, in mid-October, drawing attention from local TV stations as they prepared to make the trek to the United States. Local officials and the US Embassy in Tegucigalpa issued statements encouraging would-be migrants to turn back.

But the group continued on its journey, crossing through Guatemala and making it to Mexico.

By then, it had swelled in size – numbering more than 7,000 people, according to estimates from authorities at the time.

In Honduras, President Juan Orlando Hernandez and his administration said political opponents trying to destabilize the government were behind the so-called caravan.

Attention zeroed in on an activist and former congressman from Honduras who had been traveling with the migrants and posting updates about their journey. Bartolo Fuentes maintained he wasn’t an organizer and described the group’s formation as spontaneous.

“You are giving me some kind of superpower,” he told CNN en Español when asked whether he had organized the caravan. “There are people in this march from places I’ve never even been to. … It’s absurd to think that someone can convince all these people. … These are simply excuses because here the government doesn’t want to recognize that we have a human tragedy that people no longer can bear.”

The group’s size, he said, represented an accumulation of the same number of migrants who would ordinarily leave Honduras bit by bit, usually in much smaller groups, in any two-week period.

“Every day people leave for the United States,” Fuentes said. “The difference is, they leave in hiding. No one notices.”

Conspiracy theories surge

The group’s size – notably larger than those of other migrants who have banded together on the journey north – drew swift attention in the United States, prompting threats from Trump to slash foreign aid if migrants didn’t return home.

The absence of an organizer leading the group, or a clear explanation of how it had formed, left a void quickly filled by conspiracy theories, baseless claims and political attacks.

Trump described the group’s advance as an assault on US borders, argued its members were exploiting loopholes in asylum laws and claimed – without evidence – that Middle Easterners were in its ranks.

The US Department of Homeland Security said it knew of 270 migrants in the group with criminal histories but didn’t specify how it learned that information.

Trump, standing center stage at a campaign rally, suggested Democrats were paying people to migrate north so they’d end up with more votes. Vice President Mike Pence said he’d heard Venezuela was responsible. A Republican congressman wondered whether billionaire George Soros was bankrolling the group. A Democratic senator called the timing “unusual” and asked, “Who would this benefit if this is suddenly in the news?”

Rumors spread through tweets and Facebook posts that were swiftly shared, amplifying the message. An investigation by USA Today found that the Soros conspiracy theory had spread to hundreds of millions of social media users.

But the seeds of these conspiracy theories didn’t stay in the Twittersphere.

The suspect in the massacre at a Pittsburgh synagogue railed against Jews on social media, blaming them for the caravan’s advance. Then he allegedly headed to the synagogue and opened fire.

Trekking in flip-flops and broken sneakers

After a week traveling with the caravan, CNN witnessed little, if any, organization.

People joined and left the group at will. Exhausted by the journey, many decided to return home.

Many migrants in the group told CNN they joined at the last minute after seeing messages on social media or local news stories that inspired them to leave behind a homeland where they had long ago given up on having a future.

They walked miles in flip-flops, rubber clogs and sneakers that were falling apart.

Few appeared to have any funds. Most slept in the streets.

They told CNN they would have gone hungry if not for generous Mexicans and municipalities who offered them tamales and pineapple juice along the route.

And they said they had no choice but to flee.

“There is no work anymore. The government took our lands,” said Carlos Gomez, an out-of-work farmhand who said he’s traveling to the United States to support his eight children back home.

Chantal Alejo, a 27-year-old transgender woman traveling with the group, said a post she saw on Facebook about the caravan made her immediately pack her bag for the journey.

“There’s a lot of persecution,” she said, “and no work.”

The big questions: Why? And why now?

Such motivations have spurred migrants traveling north for years. But the groups have been far smaller.

“This one really grew bigger than anyone could have expected,” the Migration Policy Institute’s Selee said.

One possible “detonator,” Selee said, was the caravan that crossed through Mexico in April. That group sparked Twitter tirades from Trump, which brought even more publicity, creating a “demonstration effect,” Selee said.

In the case of the large group that drew Trump’s attention when it set out from Honduras last month, Allison, the professor, said it’s possible other factors – such as false rumors in a TV report about funds being available for food and transportation – contributed to the group growing to such a significant size.

“Whether that’s true or not,” he said, “you had probably thousands of people in Honduras who are considering going sometime in the next few months, or in the next year or two. It just changed their calculation about when the best time to go is.”

Usually migrants from Honduras pay smugglers thousands of dollars to guide them north. So the prospect of joining a group for free, and the reassurance of safety in numbers, is an enticing combination.

“On the one hand, it’s got to be something really bad to make you walk from Honduras to the United States,” he said. “On the other hand, it’s also, ‘Hey, here’s an opportunity for me, no matter how remote, that we might be able to get there without exposing ourselves to the financial risks and the personal risks that usually that would take.’”

Another factor: political tensions in Honduras, where President Hernandez claimed victory after a disputed election last year.

“The political crisis isn’t helping. I’m not sure it’s the reason,” Selee said. “But it is both fertile ground for activists who want to organize people to leave, and it also may create one more element of instability.”

The situation is complicated, Allison said.

“There are contradictory things that we’re still trying to tease out about the root causes,” he said.

In Honduras, for example, the murder rate – one factor analysts typically cite when they study why people migrate – has been declining.

But despite the lingering questions about these large groups forming, Allison said the most important thing to do right now isn’t to pinpoint why they’re leaving; it’s to address the humanitarian crisis that’s emerging as they make the trek

“These are people who really, with the information that they have available to them, have decided that this is their best opportunity. It’s not something they take lightly. It’s not something we should think they’re being manipulated by Honduran politicians or US politicians to do,” he said.

“We need to respond to what’s happening with both compassion and level-headedness.”

CNN’s Patrick Oppmann and Natalie Gallón contributed to this report.