Jason Petrulis is an assistant professor of U.S. history in global perspective in the department of interdisciplinary general education at California State Polytechnic University, Pomona.

Incarcerees line up for a train that will take them from the Santa Anita Assembly Center in California to a detention camp at Gila River, Ariz. in 1942. (AP Photo/National Archives)

How do you make 5,000 people disappear?

In August 1942 — 75 years ago this month — the U.S. Army removed a townful of people from Pomona, Calif., just east of downtown Los Angeles.

Over 16 days, soldiers ushered innocent women, men and children past barbed wire and bayonets, forcing them to board a Southern Pacific train for a trip to northwest Wyoming — where they were incarcerated once again. When the last train departed, more than 5,000 Japanese Americans had disappeared from California.

Then, decades later, they disappeared again, erased from their neighbors’ memories. I know this because I grew up in Los Angeles and suffered from this historical amnesia myself. Though I lived just a short drive from Pomona, I had no idea that it was one of five major sites where Japanese Americans were incarcerated in L.A. during World War II.

When I thought of Pomona, I thought of it as the location of the L.A. County Fair. The other sites had similar associations: Santa Anita was a racetrack; San Pedro was an oceanside spot; Griffith Park was home to the L.A. Zoo; and I’d never heard of Tuna Canyon. But in 1942, the U.S. government used these five sites to imprison Japanese Americans. Similar detention sites dotted the West Coast, enabling the government to remove Japanese Americans from their neighborhoods quickly and efficiently.

In 1942, Japanese Americans disappeared from their neighbors’ sight; then, across decades, they disappeared from their neighbors’ minds. Both disappearances were choices: Ordinary Americans, backed by the power of the U.S. government, decided to erase these people from their neighborhoods and these events from their memories.

That erasure reminds us that what we remember about history is not just coincidence, not just what happens to get stuck in our heads. Instead, it is a set of choices: because the events that underlie history do not change, but what we choose to remember about history does.

Above all, such erasures are an exercise of power. When Japanese Americans disappeared, it was U.S. policy to make them disappear, and the first to disappear were men born in Japan. After Pearl Harbor, FBI agents rousted Japanese American families from their beds in the middle of the night and arrested thousands of noncitizen adult men as “enemy aliens,” locking them in Griffith Park, San Pedro or Tuna Canyon. American-born Kiku Hori Funabiki remembered: “At the moment I helplessly watched my father being led away in shackles by three Federal agents, I received so deep a wound it has never healed … Was I American or wasn’t I?”

Starting in March 1942, the rest of the Japanese American population began to disappear from the West Coast, forced into “Assembly Centers,” such as Pomona and Santa Anita. It is haunting to see the maps the military made to plot its purge, carving neighborhoods into “exclusion” areas. On May 9, 1942, for instance, Exclusion Order No. 55 required 1,150 Japanese Americans to close up their businesses, secure their houses and disappear, all within a week. Along with residents of six other exclusion areas, they were forced into a newly constructed temporary detention camp on the site of the L.A. County fairgrounds: Pomona Assembly Center.

Pomona Assembly Center was a veritable town: 300 wood-and-tar paper barracks surrounded by snack bars, medical facilities, places of worship and even an athletic field. It was also a prison. Guards’ lights followed incarcerees to the bathroom at night. Curfews and censorship restricted basic freedoms. And a guard tower and a fence topped with barbed wire enforced a border, separating Japanese Americans from the rest of America.

In August 1942, after almost three months of sweltering heat and driving boredom, the residents of Pomona Assembly Center learned they would disappear again — to Heart Mountain, Wyo. They joined a larger forced migration that moved Japanese Americans from 15 temporary Assembly Centers to 10 long-term incarceration camps. In this way, the Army engineered the all-but-complete disappearance of Japanese Americans from the West Coast by fall 1942, a forced exile that lasted until the war wound down, starting in 1945. (And continued after the war: Many Japanese Americans were not welcomed home, and looked for a new start elsewhere.)

Then, in fall 2016, I watched them disappear again — this time when I started teaching at Cal Poly Pomona University in L.A. County. To mark the 75th anniversary of Japanese American incarceration, I began to work with colleagues to connect our campus to this local site of injustice. But I quickly learned that Pomona Assembly Center had disappeared from the memory of many students, faculty and staff.

How could we erase something so indelible? I found one explanation in a group of photos held at the Library of Congress, originally collected by the Army to illustrate an official 1943 report on the Assembly Centers.

The report’s 149-photo “Pictorial Summary” features scenes of Boy Scouts and basketball, meant as visual proof of the Army’s humane treatment of incarcerees. Yet while four of those published photos featured Pomona, more than two dozen other images of Pomona were preserved by the Army but not published, hiding them from public view.

A few of the unpublished photos were probably set aside because they were unremarkable, but several photos told a story the government did not want to tell. These photos (which can be viewed here and here) featured captions reading “NOT TO BE USED FOR REPUBLICATION” — evidence they had been embargoed by the government for showing the darkest side of the incarceration program.

The photos were snapped by a government photographer on one of those days of “Exodus” in mid-August 1942 when a group of incarcerees was transported from Pomona to Wyoming. And while the scene seems calm — perhaps even upbeat sometimes, judging by scattered smiles — barbed wire slices the photos in two.

Censors knew that photos of life behind barbed wire were dangerous: what would other Americans think if they saw for themselves what Pomona’s Shizuko Horiuchi saw every day? “The life here cannot be expressed,” she wrote from the Center in May 1942. “Sometimes, we are resigned to it, but when we see the barbed wire fences and the sentry tower with floodlights, it gives us a feeling of being prisoners in a ‘concentration camp.’”

It would be easy to blame government censors for the fact that my students, my colleagues and I remember so little about Pomona, but this lets us off the hook too easily. The disappearance of more than 5,000 people was not hidden. It happened in plain sight.

People lined the streets of L.A. to watch their Japanese American neighbors get stolen away to Pomona. Construction workers built a prison camp barbed wire by barbed wire. Friends, members of the clergy and even labor activists visited Pomona and observed the incarceration. In towns between California and Wyoming, people saw incarcerees whenever the train stopped for breaks. Everyone saw their disappearance; most chose not to see the evidence of injustice before them.

It’s a privilege of power to choose what you see — or to imagine that you don’t see what you actually do. Incarcerees and their families did not have this choice; they were forced to see past the barbed wire that framed their removal from yet another home. But many other Americans did have the choice to acknowledge injustice against Japanese Americans, or to ignore it.

Today, we face that choice again whenever we talk about America’s past. The stories we tell about America are made up of choices: what we honor or ignore, what we recall or forget. Indeed, when we tell stories about America’s past, we are also telling stories about who we are today, writing our own history through these choices.

The past may not change, but how we witness the past can. So this summer, as we mark the 75th anniversary of the erasure of 15 Assembly Centers, from Puyallup to Pomona, and as we struggle to acknowledge injustices around us, we can remember: You make 5,000 people disappear by choosing not to see them in front of your face.