Why did displacement differ in Vietnam, Cambodia and Laos?

The short answer

• Thirty years of war. The victors inherited countries already uprooted by almost continuous war since 1945. Fighting against French rule gave way to a conflict between the communist North and the American-backed South that spread into Laos and Cambodia. Bombing and ground fighting drove millions from the countryside into cities such as Saigon and Phnom Penh. The populations gathered there were impoverished and divided by loyalties the new rulers would punish.
• American withdrawal. American troops left under the Paris agreements of January 1973, and Congress cut aid to Saigon and Phnom Penh in 1974–75. The southern army then collapsed faster than planners expected after the North attacked in March 1975; Cambodia's government fell on 17 April. People at risk needed a way out just as the institutions meant to organize one were falling apart. Evacuation was improvised, and many were left behind.
• Revolutionary programmes. The victorious parties wanted to change the societies they now governed. Hanoi sought reunification and socialist transformation of the South; the Khmer Rouge aimed at a classless peasant nation built from Year Zero; the Pathet Lao established a socialist state aligned with Vietnam. Their plans differed, but each could identify whole classes or groups as enemies. Political victory thus became a cause of displacement, as it had in Europe in 1945.
• Alliances with the losing side. Soldiers, officials, interpreters and Hmong fighters were among hundreds of thousands who had served the old regimes or worked with Americans. Those ties could make them suspects after defeat and gave many reason to flee. The same service also gave them a claim on the foreign power they had assisted, helping explain the American evacuation and resettlement.

What it changed

Those left behind. Defeat did not end the danger for people who stayed. Hundreds of thousands of former officers and officials entered re-education camps, and city dwellers were pushed toward New Economic Zones in the countryside. Chapter 8 follows these policies and the 1978 attack on private trade into mass departures. Some unable to leave in 1975 became boat people in 1978 and 1979.

Year Zero. The evacuation of the cities began Democratic Kampuchea's attempt to remake life without money, markets, religion or families as people had known them. Forced labor, starvation and execution killed an estimated 1.5 to 2.2 million people over the next four years. Chapter 8 records the catastrophe with memorial markers and ranges of figures. Survivors reached the Thai border in 1979 after the regime fell.

Thailand on the front line. Thailand received Lao and Hmong refugees from 1975 and later Cambodians across its long land borders. Its leaders also feared Vietnamese power and communist insurgency at home. These pressures help explain a policy that was open in some years and harsh in others, and the changing colors in chapters 9 to 11. Like Austria in 1956, Thailand was a relatively small state receiving people displaced by a larger conflict.

A resettlement commitment. The first arrivals formed Vietnamese American communities and established a precedent for federal responsibility. Both helped press Washington to act when boat departures grew in 1978–79. Chapter 10 follows the Refugee Act of 1980. Earlier arrivals also sponsored relatives, giving later arrivals help in settling.