Understanding Cambodia: The Khmer Rouge History Every Visitor Should Know

Walking through Tuol Sleng on my first visit to Phnom Penh, I passed a photograph that stopped me mid-step. A young woman, maybe twenty-five, photographed at the prison intake. Her face is completely composed — no visible fear, no visible anything. It is the blankness that is unbearable. You come to understand, reading the surrounding context, that she almost certainly knew what was coming.

I stayed in front of that photograph for longer than I expected to. That moment is what Cambodia’s history does to you when you engage with it directly rather than from a comfortable distance. It makes the past specific and human rather than statistical.

This is the history every visitor to Cambodia should understand before they arrive.

What Was the Khmer Rouge?

The Khmer Rouge — “Red Khmers” in French — was a communist revolutionary movement led by Pol Pot (born Saloth Sar) that governed Cambodia from April 17, 1975 to January 7, 1979. In those three years and eight months, it implemented one of the most extreme and destructive political programs in modern history.

The ideology was a distorted agrarian Maoism that aimed to return Cambodia to what Pol Pot called “Year Zero” — a complete erasure of the existing social order and a rebuilding of society from scratch as a classless agrarian collective. Money was abolished. Cities were emptied. Schools, hospitals, and religious institutions were shuttered or destroyed. The professional classes — doctors, teachers, engineers, monks, anyone with an education or urban background — were systematically targeted for execution or worked to death in the countryside.

The movement had roots in the late 1960s, emerging from the jungles of northeastern Cambodia during a period of political instability under Prince Norodom Sihanouk and intensifying during the chaos of the US bombing campaigns and the Vietnam War era. The 1970 coup by Lon Nol, a US-backed general, destabilized the country and drove rural Cambodians toward the Khmer Rouge. When Phnom Penh fell in April 1975, the Khmer Rouge was already operating in much of the countryside.

What Happened When the Khmer Rouge Took Phnom Penh?

Within days of taking the capital on April 17, 1975, the Khmer Rouge ordered the entire population of Phnom Penh — approximately two million people — to leave the city immediately. People were told the evacuation was temporary, that American bombing was imminent. Hospital patients were pushed out in their beds. Newborns were carried from maternity wards. The sick, the elderly, and anyone unable to walk quickly enough were abandoned or killed along the road.

Phnom Penh became a ghost city within a week.

The same forced evacuation was carried out in every other urban center. Cambodia’s population was relocated to the countryside and organized into agricultural collectives — the regime’s vision of a pure agrarian communist state. Families were separated. People were reassigned to whatever collective the Khmer Rouge designated, often hundreds of kilometers from their homes. Contact between family members was forbidden or severely restricted.

Working conditions in the collectives were brutal: eighteen-hour days, inadequate food, no medical care, and constant political surveillance. Falling short of production quotas, or any sign of resistance, could mean death.

What Was S-21 and the Killing Fields?

Tuol Sleng (S-21) was a high school in Phnom Penh that the Khmer Rouge converted into a security prison in 1975. Between 14,000 and 17,000 people were imprisoned and interrogated there between 1975 and 1979. Fewer than a dozen survived.

The prison documented its victims with systematic precision — photographs of every prisoner on intake, detailed confession records extracted under torture, biographies of each person’s “crimes” against the revolution. This documentation, which the Khmer Rouge maintained obsessively, now constitutes one of the most complete records of a genocide’s mechanics in existence. It is also what makes Tuol Sleng so unbearable to walk through: the faces are individualized, named, and present in a way that abstracted statistics cannot achieve.

The Killing Fields refers to the network of sites around Cambodia where prisoners were executed and buried in mass graves. Choeung Ek, fifteen kilometers south of Phnom Penh, is the most significant of these — the primary execution site for S-21 prisoners. After the genocide, over 8,000 bodies were exhumed from the grounds. A glass memorial stupa now holds the remains, visible from the outside.

Across Cambodia, there are estimated to be over 20,000 mass burial sites. Most have never been fully excavated or documented.

How Many People Died?

Estimates vary. Scholarly consensus places the death toll at between 1.5 million and 2.2 million people — representing 20 to 25 percent of Cambodia’s entire population at the time. At least a million died from execution. The rest perished from starvation, forced labor, disease, and the deliberate denial of medical care.

The demographic consequences are still visible. Cambodia today has a notably young population — around 65 to 70 percent are under 35 — partly because an older generation was destroyed. The professional expertise that typically accumulates across generations — doctors, engineers, teachers, administrators — was eliminated almost entirely. Cambodia has been rebuilding that institutional knowledge for forty years.

How Did the Khmer Rouge End?

Vietnam invaded Cambodia in December 1978, reaching Phnom Penh on January 7, 1979. The Khmer Rouge collapsed and retreated to the jungles near the Thai border, where they continued as a guerrilla movement for nearly two more decades, backed at various points by China, the United States, and the United Nations — a geopolitical arrangement driven by Cold War calculation rather than concern for Cambodian civilians.

Pol Pot died in 1998, under house arrest by his own former comrades, never having faced international justice. The Extraordinary Chambers in the Courts of Cambodia (ECCC) — a hybrid UN-backed tribunal — was established in 2003 and has since convicted Nuon Chea (the chief ideologue) and Khieu Samphan (head of state) of genocide and crimes against humanity. Many other perpetrators died before trial, of old age or from illness, without accountability.

Why Does This Matter for Visitors?

Cambodia was a country of seven to eight million people. Between a fifth and a quarter of its population died in under four years. The generation of adults who had built expertise across medicine, education, law, engineering, and governance was nearly eliminated. The infrastructure of civil society — institutions, professional networks, knowledge bases — was systematically destroyed.

What you see in Cambodia today — the young population, the gaps in institutional memory, the visible reconstruction across every sector, the particular intensity with which Cambodians discuss their history — is directly connected to what happened between 1975 and 1979. The food markets are full because they were once emptied. The new buildings exist because the old ones were demolished or allowed to collapse. The country’s remarkable hospitality exists alongside a history that would have destroyed hospitality in many societies permanently.

How to Visit Tuol Sleng and Choeung Ek Responsibly

Tuol Sleng Genocide Museum (S-21)

The museum is in Phnom Penh, about 2 kilometers south of the Royal Palace. Opening hours are 8am–5pm daily. Entry is $10. The audio guide costs $3 and is worth hiring — it contextualizes what you are seeing in a way that a self-guided visit often misses.

Allow two to three hours, and give yourself permission to take that time rather than rushing. The courtyard, where you can sit and absorb what you have seen, is important. The museum does not sanitize its presentation: the rooms are preserved largely as they were found in 1979, and the photographs of prisoners are displayed without softening.

It is emotionally difficult. That is appropriate. It would be more concerning if it were not.

The Killing Fields of Choeung Ek

Located 15 kilometers south of central Phnom Penh. Take a tuk-tuk from Tuol Sleng — about $5-8 each way, or $15-20 for a combined tour. Entry is $6, which includes the audio guide narrated by a survivor. The audio guide is exceptional — genuinely one of the best I have encountered anywhere.

The audio tour takes approximately 90 minutes and leads you through the main burial areas, the memorial stupa, and the surrounding context. Mass grave depressions are visible throughout the grounds. Human bone and cloth fragments continue to surface after rains.

Visit Tuol Sleng before Choeung Ek. The chronological sequence matters — S-21 was the imprisonment and interrogation site; Choeung Ek was where prisoners were taken after. Understanding the prison’s function first gives Choeung Ek its full context.

A note on tone: these are sacred sites for Cambodians. Many Cambodian families lost relatives who passed through them. Respect the space — quiet voices, appropriate dress, no posed smiling photographs in front of human remains or instruments of torture.

Where to Learn More Before You Go

The books that shaped my understanding most clearly:

“First They Killed My Father” by Loung Ung is a memoir from a child’s perspective — harrowing, specific, and necessary. It was also adapted into a film by Angelina Jolie in 2017.

“When the War Was Over” by Elizabeth Becker is the authoritative journalistic account by one of the few Western journalists who visited Khmer Rouge Cambodia before its fall.

“The Gate” by François Bizot is a first-person account from the only Westerner known to have survived capture by the Khmer Rouge — a French ethnographer held in 1971, released after three months, and later trapped in the French Embassy during the fall of Phnom Penh. Extraordinary writing on an extraordinary situation.

The Documentation Center of Cambodia (DC-Cam) in Phnom Penh maintains archives and publishes research — their website is a comprehensive resource if you want to go deeper into the documented record.

Learn more about Cambodia’s depth:

• Phnom Penh — the capital and what it holds
• Siem Reap — the temple city, seen in fuller context
• Battambang — a city that survived and rebuilt
• Siem Reap Beyond Angkor — what to do when the temple pass runs out

Use the AI Trip Planner to build a Cambodia itinerary that includes adequate time in Phnom Penh.