It began with the sound of trucks, gunfire and crowds cheering. Over 50 years ago, on April 17, 1975, as the Khmer Rouge, Cambodian communist guerrillas led by Pol Pot, marched into the capital Phnom Penh, exhausted Cambodians believed the conflict was finally over and peace would finally come after five years of civil war.
Instead, it was the beginning of one of the most radical and deadly social experiments of the 20th century— a descent into terror that would claim nearly two million lives, and one-quarter of Cambodia’s population, in just under four years.
In less than 72 hours, Phnom Penh was emptied.
The memory of the deadly civil war in Cambodia
Fifty years later, the memory of those days still haunts those who survived it. “They told us to leave the city because the Americans were going to bomb us,” remembered Loung Ung, who was just five years old when the Khmer Rouge entered Cambodia’s capital. “We took a few things and walked. We didn’t know we were leaving everything behind forever.
“We are not the only family leaving the city,” Ung wrote of the time. “The soldiers are everywhere. There are so many of them around, yelling into their bullhorns, no longer smiling as I saw them before. Now they shout loud, angry words at us….”
By the end of that week, Phnom Penh, once a vibrant metropolis of nearly 2.5 million people swollen by refugees, was a ghost town. Hospitals, schools, shops, temples—all abandoned. Even the sick and dying were dragged from their beds and forced onto the roads. “The air was stifling,” wrote Dr. Haing Ngor, a physician and future Oscar winner for The Killing Fields. “The streets were filled from one side to the other. We were no longer residents of Phnom Penh. We were refugees, carrying whatever we could.
Some people died on the way. Others were shot because they couldn’t walk fast enough.
The evacuation was not a chaotic retreat but a calculated, ideologically driven purge. Khmer Rouge soldiers, often no older than teenagers, stormed into homes, hospitals, and schools shouting orders through megaphones and firing into the air. Loudspeakers repeated the same line: “Leave the city for three days. The Americans will bomb!” Fearful and war-weary citizens obeyed. Few realized it was a lie.
Entire neighborhoods emptied in hours. People streamed out on foot, pushing carts, carrying children, and dragging what little they could salvage. Medical patients were wheeled out in beds or carried on stretchers. Doctors pleaded to remain with their patients, but they too were expelled. Resistance was met with execution. In one case, Khmer Rouge fighters ordered newborns in incubators to be taken out along with their mothers; none survived.
The roads out of Phnom Penh became rivers of humanity, stretching for miles in the blistering sun. “We walked for days,” wrote survivor Daran Kravanh. “There was no water, no rest. If you stopped, you were beaten or killed. People died all around me.”
How an attack on colonialism led to genocide in Cambodia's cities
The goal of this mass expulsion was not temporary evacuation but total transformation. The Khmer Rouge viewed cities as parasites. In their eyes, Phnom Penh represented colonialism, capitalism, foreign influence, and class hierarchy. Their solution was to erase it entirely. Within 72 hours, one of Southeast Asia’s most vibrant cities was silenced, its buildings left to rot, its population dispersed.
The ideological engine driving this was a unique and extreme fusion of Maoism, xenophobia, and Cambodian peasant nationalism. Pol Pot and his comrades believed that only by destroying all remnants of modern society could they achieve true revolutionary purity. They envisioned a Cambodia where everyone labored collectively in the countryside, disconnected from the past, from religion, from foreign influence, and even from each other. Money, schools, religion, markets, and family units were abolished. People were stripped of their names, professions, and histories. Identity itself became a crime.
“This is Year Zero,” the Khmer Rouge stated. What was here before is gone. We begin again.
When the Khmer Rouge seized power, they declared it the start of “Year Zero”—a chilling decree that symbolized the erasure of everything that had come before. It was inspired by the French Revolution’s own attempt to reset history with “Year One.”
Life in the so-called "new society" quickly devolved into a nightmare. In the vast, rural labor camps, what would come to be called the Killing Fields, former doctors, teachers, artists, and shopkeepers were forced to perform backbreaking agricultural work. The workday began before dawn and ended well after dark. Meals consisted of a few spoonfuls of rice porridge. Starvation became widespread.
“There were no holidays, no rest, no medicine, no help,” recalled survivor Vann Nath. “If you got sick, you died. If you asked for food, you were accused of sabotage.”
The regime enforced silence. Speaking too much or too little was suspect. Smiling or crying could be misread as betrayal. Neighbors were encouraged to inform on each other. Children were recruited to spy on their parents. The family unit, once the cornerstone of Cambodian society, was dismantled.
The collective replaced kinship. People were sorted into mobile work brigades. Marriages were arranged en masse by the state. Even language was controlled—personal pronouns were eliminated in favor of the uniform "comrade." The Khmer Rouge even attempted to purge the language of foreign or feudal words.
Religious and cultural life was obliterated. Over 90% of Cambodia's Buddhist monks were killed or defrocked. Pagodas were destroyed or converted into barns. Theaters, schools, and libraries were burned. In their place was forced labor, indoctrination, and fear.
By 1977, paranoia within the regime had reached such extremes that the Khmer Rouge turned on its own ranks. Cadres were arrested, tortured, and sent to execution centers like Tuol Sleng, or S-21, a former high school in Phnom Penh converted into a torture prison. There, inmates were photographed, shackled, electrocuted, waterboarded, and forced to sign false confessions of working for the CIA or KGB. Of the estimated 17,000 people sent there, only a handful survived.
The Khmer Rouge’s collapse in January 1979 was as swift as its rise had been shocking. Though deeply feared, the regime was structurally hollow. Its military disorganized, its economy in ruins, and its population exhausted and resentful, all led to the easy collapse of the regime. Years of purges had decimated its own ranks, leaving leadership paranoid and the chain of command fractured. The Khmer Rouge had no air force, minimal heavy weaponry, and no real capacity to resist a large-scale invasion.
When Vietnam launched its assault in December 1978, provoked by years of cross-border attacks and an ideological rift, the Khmer Rouge forces were overwhelmed within weeks. Phnom Penh fell on January 7, 1979, with almost no organized defense.
What sealed their fate was the total alienation of the Cambodian people. The regime had terrorized its own citizens so thoroughly that few were willing to fight for it. Many even welcomed the Vietnamese as liberators. The Khmer Rouge, built on secrecy, fear, and ideological extremism, had no capacity for resilience once its control began to crack. Its leaders fled west toward the Thai border, retreating into the jungle, where they would regroup as guerrillas—but their genocidal regime was, for the time being, broken.
When Vietnamese forces invaded they uncovered what one Vietnamese officer would call “a country of death.” On entering Phnom Penh in January 1979, they found the city still eerily silent. At Tuol Sleng, the Khmer Rouge had fled just hours earlier. On the bloodstained bedframes lay 14 decomposing corpses, their throats slit, still chained by the ankles.
The Vietnamese unearthed thousands of photographs taken by the Khmer Rouge of Tuol Sleng’s victims—men, women, children, and infants, all photographed before their execution. The images are now part of the Tuol Sleng Genocide Museum, one of the world’s most chilling memorials.
Despite this overwhelming evidence, the Khmer Rouge did not vanish. Backed by China, and tacitly tolerated by the United States and its allies, who viewed the Vietnamese-installed government in Phnom Penh as a Soviet puppet, the Khmer Rouge retained Cambodia’s seat at the United Nations until 1991.
The US did not directly arm the Khmer Rouge but supported coalitions that included them, provided aid to anti-Vietnamese factions through Thailand, and helped legitimize them diplomatically during the 1980s. As historian Ben Kiernan noted: “Everyone knew the Khmer Rouge dominated the resistance. The aid flowed anyway.”
Only in the 1990s, with the Cold War over, did a reckoning begin. A UN-backed tribunal eventually tried surviving Khmer Rouge leaders. Pol Pot died in 1998, unrepentant, in a jungle compound. Others—like Comrade Duch, the head of Tuol Sleng—were finally convicted. But for many survivors, justice came too late.
Today, visitors walk through the fields of Choeung Ek, where bones still rise from the soil after rain. They pass the tree where babies were murdered and stand before glass cases filled with skulls.
And yet Cambodia endured.
Some survivors rebuilt. Others fled. People like Chum Mey, one of Tuol Sleng’s rare survivors, devoted their lives to remembrance. “I want the world to know,” he said. “Because if people forget, it can happen again.”
Fifty years on, the Khmer Rouge’s crimes remain almost incomprehensible in scale, and should never be forgotten. They were not an inevitable moment of history but the result of ideology, extremism, and a world willing, after decades of conflict in Vietnam, to look away
