On April 29, 1975, as communist North Vietnamese troops closed in on the South Vietnamese capital of Saigon, the United States ordered the immediate evacuation of U.S. personnel and several thousand South Vietnamese military and diplomatic officials. TV news cameras broadcasted harrowing images of the chaotic airlift, including crowds of desperate South Vietnamese citizens swarming the gates of the American Embassy in Saigon, soon to be renamed Ho Chi Minh City by the conquering communists.

The swift fall of Saigon in 1975 signaled the end of America’s failed military intervention in Southeast Asia, but it only marked the beginning of what would become one of the largest and longest refugee crises in history.

Over the next two decades—from 1975 to 1995—more than three million people fled Vietnam, Laos and Cambodia. Countless thousands died at sea, victims of pirates or overcrowded, makeshift boats. The lucky ones made it to refugee camps in Thailand, Malaysia or the Philippines, and more than 2.5 million refugees were eventually resettled around the world, including more than a million in the United States.

In the months following the fall of Saigon, U.S President Gerald Ford and Congress authorized the evacuation and resettlement in the United States of approximately 140,000 refugees from South Vietnam and Cambodia. But there were many hundreds of thousands more, including former members of the South Vietnamese army and their families, who faced torture and retribution from the ruling North Vietnamese.

“A common sight at the end of the war was to see South Vietnamese soldiers burning their uniforms, making sure they had no affiliation with the military whatsoever,” says Phuong Tran Nguyen, a history professor at California State University, Monterey Bay, and author of Becoming Refugee American: The Politics of Rescue in Little Saigon.

South Vietnamese intellectuals and other potential enemies of the revolution were rounded up and shipped off to “reeducation” camps, which were really forced labor camps designed to break the will of the South Vietnamese and indoctrinate them with communist ideologies. Many residents of Saigon, the former South Vietnamese capital, were forced to move to the countryside to labor on collective farms. In neighboring Cambodia, the Khmer Rouge seized power and began a brutal campaign of imprisonment and mass executions of its enemies.

As the political and economic situations deteriorated in Vietnam, Laos and Cambodia, the steady trickle of refugees fleeing the region became a torrent. Desperate families packed their belongings in a single suitcase and fled their homes “by any means available,” says Long Bui, a professor of international studies at the University of California Irvine and author of Returns of War: South Vietnam and the Price of Refugee Memory.

“Some of them trekked through the forest through Laos and into Thailand, but mostly they fled by ocean to places like Singapore and Hong Kong,” says Bui. “They were often attacked by Malaysian and Thai pirates who raped the women and stole any gold or money they had. That’s why it was so harrowing.”

These “boat people,” as the refugees became known, weren’t welcomed or even recognized as refugees by most countries in the region. None of the nations in Southeast Asia had signed on to the United Nations Refugee Convention, for example, and some were openly hostile to the tens of thousands of Vietnamese and Cambodians who were threatening to overwhelm their limited resources. By 1979, when more than 50,000 refugees were arriving by boat every month, countries like Malaysia and Singapore began physically pushing boats full of refugees back into the sea.

“It’s estimated that between 25,000 and 50,000 boat people perished at sea,” says Nguyen. “They were out for days without almost any food or water, and a lot of the women and children couldn't swim.”

After an emergency 1979 UN conference to address the refugee crisis, deals were struck to safely house the refugees in places like Malaysia, the Philippines and Indonesia, and protocols were implemented to speed refugee resettlement in countries like the United States, Australia, France and Canada. From July 1979 to July 1982, more than 620,000 refugees were permanently resettled in more than 20 countries, but families often spent years waiting in refugee camps.

The Pulau Bidong refugee camp in Malaysia was typical of the conditions faced by many refugees. Measuring only 1 square kilometer in area, the camp was designed to house 4,500 people, but swelled to 40,000 residents in June of 1979, making it the most heavily populated place in the world. Charitable organizations and NGOs ran clothing and toy drives for the refugees, but overcrowded conditions and poor sanitation were constant challenges.

Most refugees could expect to stay in the camps months or even years before being slated for resettlement. As the day approached to leave for their new lives, they’d be given English classes and acquainted with some of the customs of their new homes. Some of these camps were in operation to serve a continuous stream of refugees throughout the 1980s and into the mid-1990s.

“Some of the camps in the Philippines didn’t close until the early 2000s,” says Bui, “which means that multiple generations were born inside refugee camps.”

It wasn’t until 2005, for example, that the last of the 250,000 documented “boat people” who arrived in Malaysia from Vietnam were finally resettled some 30 years after the fall of Saigon.

Refugees from Southeast Asia were resettled in the United States in waves. The first wave arrived in 1975 as part of President Ford’s initial 140,000 evacuees. Those refugees, most of whom were educated and spoke some English, received a warm welcome from an American public eager to absolve some of its guilt over the military’s sudden exit from South Vietnam.

The second wave of refugees, which began arriving in the United States in 1978, received a colder reception. These were the so-called “boat people,” generally poorer and less educated with a large contingent of single men. Because of the trauma they suffered in escaping a war-torn homeland and surviving sea crossings and refugee camps, many of these second-wave refugees had a harder time adjusting to life in America. To make matters worse, the American public’s support for refugees had waned by 1978 as the economy sunk into a recession.

“The majority of Americans didn’t want the Vietnamese here,” says Bui. “The refugees were a stark reminder of a lost war and were seen as an economic burden. It wasn’t a very welcoming climate.”

From 1979 to 1999, an additional 500,000 refugees arrived as part of the UN’s Orderly Departure Program, which made it possible for refugees to migrate directly from Vietnam to the United States. Many of these refugees had spent years as political prisoners and in reeducation camps, traumatic experiences that they tried to put behind them as they restarted their lives in a sometimes hostile land.

“I was born in the U.S., but the refugee experience of my parents still shaped my life,” says Bui. “I went to 16 different schools from K to 12. We never really settled. We still carried economic issues and poverty that we got from the war. My story is a second-generation story but it carries over from the refugee history.”

The world was unprepared for the large-scale refugee crisis that followed the abrupt end of the Vietnam War. The crisis forced the United Nations and member countries like the United States to clearly define who qualifies as a refugee and to draw up policies and procedures for granting asylum to people fleeing violence and oppression. But for historians like Nguyen, it feels like the real lessons of Vietnam were never fully learned.

“The United States doesn’t take enough into account how refugee migration and displacement are a part of all of our foreign policy interventions,” says Nguyen. “Any kind of war will lead to that. We need to be prepared to handle the humanitarian crisis that inevitably follows the military component.”