The caravan of immigrants traveling through Mexico this April was organized by Pueblos Sin Fronteras, which has also done this in previous years, although not all the way to the US border. President Trump seized on a story originally published by BuzzFeed and then used the caravan as a pretext to send US National Guard troops to the border.

I went to northwestern Mexico to photograph a portion of the caravan’s journey north to Tijuana. They were mostly families seeking political asylum in the United States, although many applied for asylum in Mexico. They were escaping violent conditions in their home countries, chief among them Honduras, where gang violence and political instability have become, for many people, increasingly impossible to live with. Many families had to flee suddenly, with few possessions.

In Honduras, the US government supported the 2009 right-wing coup and the presidential incumbent in the disputed 2017 election. The resulting insecurity and clashes there, combined with gang and drug violence, have driven migration from that country.

MS-13 originated in Los Angeles in the 1980s in the immigrant Salvadoran community. In subsequent years many members were convicted of crimes and deported back to El Salvador, where they spread the gang to their home country. The “Maras” are now powerful throughout much of Central America, primarily in the “Northern Triangle” countries of El Salvador, Guatemala, and Honduras.

In the United States, MS-13 has grown in some Central American immigrant communities, which is ironic and sad, as so many asylum seekers fled their countries to the US to escape the Maras. MS-13 has committed crimes, including murder, in various US communities, and federal law enforcement, including ICE, has gone after them. President Trump recently referred to them as “animals.” The dragnet, though, has swept up many undocumented immigrants who had nothing to do with gangs. ICE sometimes refers to these people as “collaterals,” and although they may not have been gang members themselves, once they are in detention, they are subject to deportation due to current Trump administration policies.

In the case of Arizona Border Recon, many of the volunteers are former military or law enforcement officers. They go for week-long operations on the border for what they consider patriotic reasons.

That said, they don’t train together, and any military or police unit that does not train together will never be an effective force. In the case of their surveillance ops on the border, the smugglers will often just wait them out. Even if AZBR volunteers stop someone crossing, they don’t have the authority to actually detain them, but rather just to call the Border Patrol. So, in that sense, they aren’t vigilantes, as they can’t actually do much more than surveil, delay — and look tough.

I think we have to separate purpose from motivation. It’s quite possible that the purpose of these groups is likely as stated — to deter human and drug trafficking along the border. Their motivation, however, depends very much on the particular volunteer, and may come from much darker places.

Both CoreCivic and the GEO Group donated heavily to the Trump campaign, according to press reports, and their stock prices shot up when he won the presidency. These for-profit prison corporations make money every time ICE sends them new immigrants for detention. Many of the immigrants they receive from ICE have been longtime residents of the United States and actively try to fight deportation in immigration courts.

While they are awaiting their trials, many are housed in these prisons, which are scattered across the United States. It’s lucrative business for the prison corporations. I should mention that both CoreCivic and the Geo Group also house many thousands of criminal prisoners who are non-immigrants. The United States incarcerates more people than any other country and it’s big money.

I think that we are in a golden age of photography. Much has been said of the negative aspects of everybody thinking they are a photographer, just because they use the camera in their phones. Well, I look at this another way: I think that people are more visually literate than ever and that the use of phone cameras has created a great interest in photography in general. I believe that people do appreciate the difference between an amateur photo and a professional piece of photography. That’s why Getty Images matters and is doing so well, even if many newspapers have struggled in the last decade.

So, yes, the camera and the images it creates, whether from my professional Canon DLSR cameras or my iPhone (which I also use professionally for video), is a powerful tool in the hands of a human witness. As a photojournalist, that is my job: to document history as it happens and shed light on the moments that would otherwise remain unseen, and that includes showing many sides of the story.

That notwithstanding, words matter too; otherwise I wouldn’t have taken the great effort to have all the captions and essays in both English and Spanish. I wanted this book to be accessible to more people, and, frankly, I thought it would have been insulting to do a book on undocumented immigration from Latin America in only English.

The undocumented immigrants of today on the receiving end of intolerance and xenophobia are not all that unique in US history. Nationalist attitudes have surfaced time and again as waves of immigrants have come to America for a better life. In the 1950s the Eisenhower Administration deported a million Mexicans in what they officially called “Operation Wetback.” That was the official name!

During the Trump campaign, I spoke with numerous immigrants, both documented and undocumented, and they were very concerned that Trump would be elected president. I told them it was doubtful, but they insisted and were preparing for it. They were right, because they’d seen it all before.