When immigration detention becomes a system of concentration: Lessons from research on 150 historical cases

The phrase "concentration camp" is freighted with dark historical meaning. Most people hear it and instinctively think of concentration camps used by the Nazis to exterminate Jews and other minority populations during the Holocaust.

But the use and name of concentration camps originated far earlier. In the late 1800s, Spanish military officials used concentration camps – reconcentrados – during their 1896–97 Cuban campaign to isolate civilians from rebels, resulting in widespread death and disease.

We are scholars whose research into international relations and conflict includes studying historical and modern uses of these systems of camps as a form of repression.

In recent peer-reviewed research, we identified four characteristics that define what qualifies as a concentration camp system : targeting groups of civilians for imprisonment; enclosed spaces where the state controls who enters and exits; departure from standard detention practices; and abuse and neglect. We then created a dataset detailing 150 systems of camps used globally since 1896 that fit this criteria. This includes the U.S. internment of more than 125,000 Japanese immigrants and Japanese American citizens during World War II, the Argentine military junta's use of camps in their mid-1970s campaign to reorganize society, and Vladimir Putin's use of so-called filtration camps in Russia's war against Ukraine.

Our use of the term "concentration camp" is not meant to sensationalize or diminish its historical meaning, particularly as it relates to the Holocaust.

Rather, identifying such systems early is how the concept of "never again " – the promise to prevent mass atrocities, such as genocide, and combat extremism – can be translated into meaningful policy action from the public and policymakers.

Based on our criteria, we believe the network of detention facilities maintained by U.S. Immigration and Customs Enforcement fits into this broader definition of a system of concentration camps.

The evolution of concentration camps

After the use of concentration camps by the Spanish in Cuba, British officials adopted the practice in southern Africa during their counterinsurgency campaign against the Boer population – descendants of Dutch, French and German Protestant settlers – at the turn of the 20th century. The British detained 110,000 Boers and 37,000 indigenous Blacks in their network of 120 camps. At least 27,000 Boers and 14,000 Blacks died as a result of rampant disease and insufficient food supplies.

By the time major German military operations in Eastern Europe began in 1939, states around the world had erected more than 30 systems of concentration camps, according to our research .

Yet the term soon took on an even darker meaning. Concentration camps were employed most infamously as part of the Nazi regime's brutal genocide in the 1930s and '40s. In its 12 years in power, the Nazi government opened more than 1,000 concentration camps in which it detained millions of individuals. In addition to facilitating the Nazi Holocaust and other group-targeted violence against minoritized and non-German populations, Nazi security forces used the camps to repress political opposition and provide labor to the German civilian and military economies.

Though few camp systems have reached the severity or scale of those used during the Holocaust, modern camps often pursue similar goals of ethnic cleansing and forced displacement, practices such as torture and an absence of due process.

In our study, we found 93 examples of systems of concentration camps used since the conclusion of World War II. This includes more than 1,200 camps erected by Chinese authorities in Xinjiang province as part of an expansive policy of discrimination against the Uyghur population there. The Chinese government has detained more than 1 million Muslim Uyghurs since at least 2017, stripping them of their traditions, cultures and languages.

Our 4 criteria further explained

Our research confirms that the word "concentration" is critical to describing these camps. Two key criteria of the camps are the concentration of large numbers of targeted civilians into spaces, which are then secured by small numbers of captors who control who enters and exits the camps.

A third criteria we examined identifies concentration camps as "irregular" insofar as they operate outside of legal frameworks that regulate prisons, refugee camps and immigration detention centers. Concentration camps are run by separate authorities that deny detainees due process, such as formal criminal charges, legal representation or a fair trial.

The last criteria we used as we evaluated camps was the presence of squalor and routine violence. Specifically, we looked for evidence that detainees regularly experienced at least two forms of abuse, including but not limited to torture, beatings, mass killing, sexual violence, psychological abuse, lack of food, lack of water, lack of shelter, lack of healthcare, overcrowding and spread of disease.

ICE detention centers

As of April 2026, there are more than 240 active ICE detention facilities across the U.S.

Migrants held in these camps are not free to leave, though some are given a choice: self-deport − agreeing to leave the country immediately − or remain in custody. Since the beginning of Trump's second term, migrants have filed more than 34,000 habeas corpus petitions challenging their confinement without trial, exercising a constitutional right.

Based on the criteria we developed, ICE detention camps fit in the spectrum of a system of concentration camps.

Starting with the first criteria, groups of civilians are being targeted by ICE, often based on their perceived ethnicity.

Though ICE's stated mission is to detain those without documented legal status, many arrests have been based on physical appearance and location rather than evidence of unlawful presence in the United States.

More than 272,000 people arrested by ICE in the first six months of Trump's second term were booked into ICE detention facilities. While deportations are increasing at a rapid rate , at least 60,000 people remain in detention facilities as of April 2026 – neither released nor deported. These numbers easily exceed counts of individuals held in immigrant detention centers in earlier years.

Hundreds of U.S. citizens have been detained , without justification and against their will, by ICE. The number of individuals arrested in homes and communities, often without an arrest warrant signed by a judge, reached more than 400 people per day in October 2025 .

In terms of the second part of our definition, these people are being concentrated in spaces where the Trump administration controls who, when and under what conditions people may enter or exit these facilities. Access has been restricted for lawyers , family members of migrants , journalists and members of Congress .

As for the third criteria, the ICE detention centers also operate separately from the U.S. Federal Bureau of Prisons. ICE detention is managed by the Office of Enforcement and Removal Operations under the Department of Homeland Security, in collaboration with private prison companies .

As of April 2026, more than 70% of migrants had no criminal conviction , while many of the remainder were held for minor offenses, such as traffic violations. Failure to provide trials for migrants, particularly those who do not pose these risks, is a departure from established norms.

Our framework's final criterion is purposeful abuse or neglect. This includes the practice of inflicting direct physical harm or the failure to provide basic necessities – food, water, shelter, healthcare.

Numerous reports have highlighted cutoffs in payments to third-party medical providers who gave care to detainees and a 36% decline in mandated detention facility inspections by ICE's internal Office of Detention Oversight. These actions have resulted in unsanitary conditions and medical neglect in these facilities. Twenty-three deaths were reported between October 2025 and March 2026, putting the current fiscal year on pace to be the deadliest in over 20 years.

As scholars, we argue that ICE detention centers meet the criteria for concentration camps. We do so not to be provocative but to provide precise language, rather than euphemisms, so people can heed the warnings of atrocities committed in the past.

As journalist Andrea Pitzer argues in her writing about concentration camps , the longer camps exist , the more they shift from a transient emergency measure to a permanent pillar of state function.

Malia Hirasa and Sydney Horton , undergraduate students at the University of Arizona, contributed to this story.

This article is republished from The Conversation , a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Alex Braithwaite , University of Arizona and Rachel D. Van Nostrand , Louisiana State University

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Alex Braithwaite received funding from the US National Science Foundation (NSF) through grant award 2213615.

Rachel D. Van Nostrand does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

The Conversation

This story was originally published May 1, 2026 at 8:04 AM.