The president has now announced that all US and allied troops will be withdrawn from Afghanistan by September 11, 2021, the 20th anniversary of the 9/11 attacks. The ground war in Afghanistan is therefore now ending and, with the end of that war, ends the justification for continuing to detain the men captured for allegedly fighting against us in that war.

Twenty-eight of the men still detained at the Guantánamo Bay detention camp fall into that category. Unlike the others detained at Guantánamo who are charged with terrorism-related crimes, these 28 men are not accused of participating or assisting in the 9/11 attacks or of engaging in or supporting any other acts of terrorism. Rather, they are detained as “law-of-war” detainees, on the assertion that they participated in or supported military forces fighting against the United States and our allies in Afghanistan almost 20 years ago.

The Supreme Court affirmed the authority to detain these men in the Hamdi v. Rumsfeld case, decided in 2004. In her plurality opinion in that case, Justice Sandra Day O’Connor found that, although the congressionally passed 2001 Authorization for the Use of Military Force (AUMF) contains no explicit authorization to detain, the detention of individuals “who fought against the United States in Afghanistan…for the duration of the particular conflict in which they were captured, is…an exercise of the ‘necessary and appropriate force’ Congress has authorized the President to use.” Relying on long-standing international law-of-war principles, Justice O’Connor pointed out that the purpose of the detentions is to prevent the individuals from returning to the battlefield and that “‘[c]aptivity is neither a punishment nor an act of vengeance,’ but ‘merely a temporary detention which is devoid of all penal character.’”

The opinion recognized that the current conflict was unlikely to end with a formal peace treaty, but emphasized that the detentions could not last forever. The detention authority extends only “for the duration of the particular conflict in which [the individuals] were captured,” and “[i]t is a clearly established principle of the law of war that detention may last no longer than active hostilities.” Thus, “the detaining country must release and repatriate [the detained individuals] ‘without delay after the cessation of active hostilities,’ unless they are being lawfully prosecuted or have been lawfully convicted of crimes and are serving sentences.’”

The opinion found that continued detention of individuals who fought against the United States in Afghanistan is authorized “if the record establishes that United States troops are still involved in active combat in Afghanistan.”

With the withdrawal of United States troops from active combat in Afghanistan, that authorization is now ending, and the 28 men at Guantánamo not charged criminally as terrorists but detained only as combatants in the military hostilities in Afghanistan should be allowed to return home.

That result is not only compelled by law; it is right and just. Afghanistan has been our nation’s longest war and, as a result, these men have been held in law-of-war detention for almost two decades, longer than any others in US history. And had they been charged and convicted of providing material support for terrorism, rather than simply of fighting in Afghanistan, they would in all likelihood have already served their sentences and been released. Perversely, these men are being treated worse than those we have actually charged as terrorists.

Repatriating these men would be an important first step in closing the Guantánamo prison. That prison continues to be used effectively by terrorists to recruit followers to their cause. It is also enormously expensive, costing well over half a billion dollars a year to operate. Closing the prison would enhance our security and relieve taxpayers of that wasteful burden. As a first step, these 28 men not charged with participating in or supporting terrorist activity should now be transferred home.