After 20 years of fighting, the U.S.-backed regime in Afghanistan has rapidly collapsed. The Taliban has taken over the country for a second time, and its arrival in Kabul triggered panic. As the remaining Americans and thousands of Afghans converged on the airport, desperate scenes unfolded. Multiple people died in the chaos, including some who plunged to their deaths from the air while trying to board departing planes, and the images sparked immediate comparisons to the scenes of South Vietnamese fleeing Saigon. An urgent question resonates between our past and present: What will be the fate of those aligned with the United States?

Over 300,000 Afghan civilians have worked with the U.S. in a variety of occupations, including as interpreters and construction workers, according to the International Rescue Committee. At least 18,000 have begun the paperwork to apply for special immigrant visas (SIV) which would allow them to enter the United States but are awaiting final approvals. Taking into account that their immediate families will also need evacuation, the number swells to an estimated 70,000 people in the SIV pipeline. There are so many Afghans who have a reasonable claim to U.S. assistance but who do not qualify for a SIV that the State Department created a Priority 2 designation — intended for activists, journalists and humanitarian aid workers, among others — in early August. Still, the number of Afghans who fear for their lives and want to leave far eclipse the spots available via either designation.

The history of the Vietnam War suggests that refugee safety is more than an acute emergency: The question of what we owe those affected by our wars lingers for decades.

In early 1975, North Vietnam launched a decisive military offensive. Vast swaths of South Vietnamese territory fell rapidly. When, on March 29, communist troops captured Da Nang, a bustling port metropolis and South Vietnam’s second-largest city, officials in Washington and Saigon frantically planned a belated evacuation. The extent and nature of the U.S. obligation to its Vietnamese allies was an immediate and consistent part of these conversations. Efforts to include the South Vietnamese in U.S. evacuation plans faced considerable domestic opposition: War fatigue, economic woes, racism and the tendency to see Vietnamese people as enemies rather than allies all added to the impulse to get the last Americans out and wash the nation’s hands of the conflict.

Still, in April 1975, 130,000 Vietnamese were evacuated alongside American personnel. The chaos on the ground and the limited number of seats meant that those who resettled in the United States endured a traumatic separation from close family members, who faced incredibly difficult conditions in Vietnam. In the 20 years after the withdrawal, the government directly admitted another half-million individuals with familial and employment ties to the United States through the Orderly Departure Program (ODP). The program allowed this group to leave without the dangers of clandestine flight. After years of negotiations and pressure from NGOs, Vietnam permitted Amerasians (the children of Vietnamese women and American men), those formerly interned in Hanoi’s reeducation camps and their close family members to emigrate through subprograms of the ODP.

While many American allies remained trapped in Vietnam, others fled — or, in some instances, were expelled — to neighboring countries. The years following the installation of communist governments in Vietnam, Laos and Cambodia saw one of the largest migrations of the 20th century. Between 1975 and 1979, more than 700,000 people reached the shores of first asylum nations. By 1995, the total number of migrants stemming from the conflicts exceeded 1.4 million. At international conferences in 1979 and 1989 aimed at addressing Southeast Asian migrants, Washington accepted the largest number of refugees — around 823,000 — and pledged the most money to support the United Nations’ refugee programs.

Eventually, more than 1 million Vietnamese — universally called “refugees” but occupying a variety of legal categories — resettled in the United States, in addition to hundreds of thousands of Laotians and Cambodians. Facilitating these migrations required negotiating agreements with Hanoi in the absence of formal diplomatic relations and, often, revising U.S. laws. The administrations of Presidents Jimmy Carter, Ronald Reagan, George H.W. Bush and Bill Clinton all supported these resettlements. How do we explain this sustained, bipartisan support, which occurred even as the United States adopted far less generous policies toward migrants from other countries?

The highly visible plight of people who fled by sea and revelations of genocide in Cambodia helped prompt action — especially as people around the world confronted the brutal history of the Holocaust. (In a 1979 speech, Vice President Walter Mondale suggested that a failure to respond would be equal to the failure to act to save European Jews on the eve of World War II.) Lawmakers with stark political differences eventually found a common cause in refugee resettlement. Sens. Bob Dole (R-Kan.) and Ted Kennedy (D-Mass.) co-sponsored resolutions that received unanimous support, a level of consensus usually unheard of for a topic related to the Vietnam War. For those who opposed the war, assisting those paying the price for U.S. policy failures seemed an obvious choice and a moral necessity. For those who supported U.S. escalation and remained committed to waging the Cold War, the fact that so many Vietnamese fled their homeland served as a substitute for military victory insofar as it seemed to validate the claim that the war had been a “noble cause” all along.

Finally, the tireless work of nongovernmental actors helped keep these questions in front of U.S. officials. The successive waves of migration programs after 1975 were not automatic but instead resulted from hard-fought, intentional lobbying and policymaking.

As in 1975, the U.S. government has pledged to include Afghan allies in its evacuation plans. In mid-July, the Pentagon announced Operation Allies Refuge, a program to provide relocation flights for those approved under the SIV program. Those flights began July 30, but their pace has not kept up with the Taliban’s advance. As with the evacuation of Saigon, the military situation in Kabul deteriorated so quickly that belatedly made plans were poorly executed.

Pressures to prolong and expand the evacuation are rising. On Tuesday, a bipartisan group of 40 lawmakers sent President Biden a letter asking the United States to “do everything possible” to secure the airport “until the rescue mission is complete and our citizens, allies, and vulnerable Afghans have had an opportunity to leave.” The authors included Republican hawks and Democrats who have been pushing for an end to the war for years. The lawmakers directly challenged the president’s timetable, urging that the goal of leaving by Aug. 31 should not apply to the rescue effort and that the United States should stay “as long as is necessary to complete it.” President Gerald Ford received a similar letter in 1975. But much has changed since then.

So many South Vietnamese were able to evacuate with the United States in 1975 because American officials were willing to postpone most procedural formalities. Throughout that April, many lower-ranking U.S. officials, skeptical about their government’s willingness to evacuate allies, snuck out their friends and colleagues on clandestine flights, which often bent if not outright broke immigration laws. (In my research, building on Thurston Clarke’s work in “Honorable Exit,” I found that most of these actions had the tacit approval of high-ranking officials in Washington and Saigon, who publicly stated that evacuation plans were merely cautionary, even though they privately knew that the country would fall.) The tumultuousness of April 1975 also meant that many South Vietnamese evacuated by chance and did not have formal documents. They were paroled into the United States as a group, with individual processing following thereafter.

The laws governing refugee admissions have grown more numerous and more complex since then: Domestic and international refugee norms now favor individual screenings, and the paperwork for a special immigrant visa or other legal paths to the United States is substantial. In his address to the nation Monday, Biden gave no indication that he would override procedural requirements for SIVs or other avenues to the United States, stating that the United States would airlift only “eligible” Afghans. Thus far the White House has been either unable or unwilling to supersede legal formalities as previous administrations did.

Policy norms have also shifted notably. While xenophobia has been a potent force throughout U.S. history, the Trump administration set the annual cap for refugees at a historic low last year: 15,000. The Biden administration initially intended to retain this record-low number until pressure from Democratic constituents prompted an increase to 62,500 for this fiscal year. Historically speaking, this figure is also small, especially considering the dramatic increase in the number of displaced peoples around the world. The annual ceiling for refugee admissions during the Reagan years, for instance, ranged from 70,000 to 217,000. Given these trends, it is unclear how many Afghans the United States will ultimately be willing to resettle.

As Americans grapple with the loss in Afghanistan, there will be a tendency to ask questions in the past tense: What could have been done differently? Was another outcome possible? For many Afghan allies, however, the war is not over; for them, the most urgent questions remain in the present. What does the United States owe the people with whom it’s been aligned for decades? How much effort is it willing to expend, despite public indifference or even opposition, to facilitate their departure and resettlement? The most pressing “lesson of Vietnam” is that these questions should stay with us long after the evacuation of the last Americans from Kabul.

This story has been updated for print.