Past Occupations of Cambodia by Siam (Thailand) and Some Cambodian History

Provinces that were occupied by Thailand (Siam) — and when

1) Battambang

  • Occupied: 1795 – 1907
  • Again: 1941 – 1946
  • Details:
    • First period: Siam took control after weakening of the Khmer kingdom.
    • Returned to Cambodia under French colonial pressure in 1907.
    • Second period: Re-occupied by Thailand during WWII after the Franco-Thai War.

2) Siem Reap

  • Occupied: 1795 – 1907
  • Again: 1941 – 1946
  • Details:
    • Controlled together with Battambang as part of western Cambodia.
    • Included Angkor, which was under Siamese rule for over a century.

3) Sisophon area

(today mostly Banteay Meanchey)

  • Occupied: 1795 – 1907
  • Again: 1941 – 1946
  • Details:
    • Was not a separate province then, but part of the Battambang–Siem Reap region.

4) Parts of Koh Kong

  • Occupied: early 1800s – 1907
  • Details:
    • Coastal areas were administered from Siam (Trat region).
    • Returned to Cambodia under the 1907 Franco-Siamese treaty.

The two main occupation periods explained

First period: 1795–1907

Siam controlled much of north-western Cambodia:

  • Battambang
  • Siem Reap
  • Sisophon region
  • Parts of Koh Kong

These areas were ruled by Khmer governors loyal to Siam.
They were returned to Cambodia when France forced Siam to cede them in exchange for other territory.


Second period: 1941–1946

During World War II:

  • Thailand, backed by Japan, re-occupied western Cambodia after defeating French Indochina.
  • Provinces taken:
    • Battambang
    • Siem Reap
    • Sisophon area
  • After Japan’s defeat, Thailand was forced to return all territory to Cambodia in 1946.

Quick summary table

Cambodian areaOccupied by ThailandReturned to Cambodia
Battambang1795–1907, 1941–19461907, 1946
Siem Reap1795–1907, 1941–19461907, 1946
Sisophon / Banteay Meanchey1795–1907, 1941–19461907, 1946
Parts of Koh Kongearly 1800s–19071907

Thailand (formerly known as Siam) has a history of territorial disputes and control over parts of what is now Cambodia, stemming from centuries of regional conflicts. The most notable periods of occupation involving specific provinces are as follows:

1794–1907: Siamese Control of Western Cambodian Provinces

In 1794, Siam acquired control over the Cambodian provinces of Battambang (Bătdâmbâng) and Siem Reap (Siĕmréab), including the area around Sisophon (now part of Banteay Meanchey province), as part of an agreement to install a Cambodian prince on the throne. These territories remained under Siamese administration for over a century, during which Cambodia was often treated as a vassal state amid broader Siamese-Vietnamese rivalries. In 1907, under a Franco-Siamese treaty, Siam ceded these provinces back to French Indochina (which controlled Cambodia at the time).

1941–1946: Thai Annexation During World War II

Amid the Franco-Thai War (October 1940–January 1941) and with Japanese support, Thai forces invaded and occupied disputed territories in French Indochina, including parts of Cambodia. Occupation began in earnest on January 5, 1941, and a Tokyo-mediated peace treaty on May 9, 1941, formalized the annexation of the following areas, which Thailand reorganized into new provinces:

When did the Khmer empire become Cambodia?

Short answer: there was no single day when the Khmer Empire “became” Cambodia — it was a long transition that happened over several centuries.

But we can pin down the key turning points.


The clear timeline

1) Khmer Empire

  • Dates: ~802 – 1431
  • Capital: Angkor
  • This is when Cambodia was a major regional power.

2) Fall of Angkor → Kingdom of Cambodia

  • Turning point: 1431
  • Angkor was sacked by Ayutthaya (Siam).
  • The capital moved south to Phnom Penh / Longvek.
  • From this point on, the state is no longer an empire — it becomes what historians call the Kingdom of Cambodia.

This is the moment most scholars mark as:

The end of the Khmer Empire and the beginning of Cambodia as a kingdom-state.


3) Modern Cambodia begins

  • 1863 – Cambodia becomes a French protectorate.
    This is when borders, administration, and the modern state structure really take shape.
  • 1953 – Cambodia becomes fully independent.
  • Since then: the modern nation-state of Cambodia.

So what’s the real answer?

It depends what you mean by Cambodia:

Meaning of “Cambodia”When it begins
Khmer people & cultureOver 1,000 years ago
Political state after Angkor1431
Modern nation-state1863–1953

Best simple answer

If someone asks this in plain language, the most accurate and useful reply is:

The Khmer Empire ended in the 1400s. After the fall of Angkor in 1431, the empire slowly became the Kingdom of Cambodia, which later developed into the modern country of Cambodia.

Please explain how Cambodia survived between powerful neighbors (Siam and Vietnam) after the empire fell.

This is one of the most important — and least appreciated — parts of Cambodian history.
After Angkor fell, Cambodia didn’t survive by strength. It survived by adaptability.

Here’s the clear story.


How Cambodia survived between Siam and Vietnam

The situation after 1431

When Angkor fell, Cambodia lost:

  • Military dominance
  • Population centers
  • Economic power

At the same time, two aggressive neighbors were rising:

  • Siam (Thailand) from the west
  • Vietnam from the east

Cambodia sat right between them — the worst possible position.

From then on, Cambodian survival depended on diplomacy, balance, and endurance, not conquest.


Strategy #1 — Playing Siam and Vietnam against each other

Cambodian kings learned a hard rule:

Never let one neighbor become too strong over Cambodia.

So they constantly shifted alliances:

  • When Siam pressured → lean toward Vietnam
  • When Vietnam pressured → lean toward Siam

This wasn’t weakness. It was realpolitik — survival politics.

Yes, it meant:

  • Paying tribute
  • Accepting influence
  • Sometimes installing kings backed by one side or the other

But it kept Cambodia alive as a state, not erased from the map.


Strategy #2 — Moving the capital to survive

After Angkor:

  • Capital moved to Longvek, then Oudong, then Phnom Penh.

Why?

  • Safer from Siamese attacks
  • Better access to rivers and trade
  • Easier to maneuver diplomatically

This shift south is one reason Cambodia still exists today.
If leaders had tried to hold Angkor at all costs, the kingdom likely would have been destroyed.


Strategy #3 — Accepting temporary loss to avoid total loss

Cambodia often:

  • Lost provinces
  • Lost control of kings
  • Lost independence for periods

But it never accepted extinction.

Examples:

  • Western provinces lost to Siam → later recovered
  • Eastern lands lost to Vietnam → some absorbed permanently, but core survived
  • Periods of Siamese or Vietnamese dominance → followed by restoration

Cambodia chose:

Better to bend than to disappear.

That choice kept Khmer identity alive when many smaller kingdoms vanished.


Strategy #4 — Using France as a shield

By the 1800s, Cambodia was close to being fully swallowed:

  • Siam controlled the west
  • Vietnam dominated the east
  • Cambodian kings were nearly powerless

So King Norodom made a desperate but smart move:

  • 1863 — Cambodia accepts French protection

This cost sovereignty — but saved the country.

France:

  • Forced Siam to return Battambang and Siem Reap
  • Stopped Vietnam from absorbing Cambodia
  • Fixed borders that still exist today

Colonialism wasn’t kind — but in Cambodia’s case, it prevented national extinction.


Strategy #5 — Cultural survival even when political power was weak

Even when Cambodia was controlled or pressured:

  • Khmer language survived
  • Buddhism survived
  • Royal tradition survived
  • Identity survived

Empires fall.
Cultures that adapt endure.

That’s the real miracle of Cambodia.


The honest bottom line

Cambodia survived because it learned to:

  • Negotiate instead of dominate
  • Endure instead of conquer
  • Adapt instead of collapse

Other kingdoms in Southeast Asia vanished completely.
Cambodia didn’t — not because it was strongest, but because it was most resilient.

Please walk me through a short timeline of the most dangerous moments when Cambodia almost disappeared.

Here’s a short, clear timeline of the most dangerous points.


The moments Cambodia almost vanished

1) 1431 — Fall of Angkor

Threat: Total collapse after empire falls
Danger: Very high

  • Angkor is sacked by Ayutthaya.
  • Population scatters, power breaks down.
  • Many kingdoms in this situation simply die out.

Why Cambodia survived:
Leaders abandoned the ruins instead of clinging to the past and rebuilt farther south.
Painful move — but smart.


2) 1594 — Siam captures Longvek

Threat: Annexation by Siam
Danger: Extreme

  • Longvek, the new capital, is destroyed.
  • Thousands of Cambodians taken as captives to Siam.
  • Cambodia loses control of its own kings for years.

Why Cambodia survived:
The kingdom accepted vassal status instead of extinction.
Weak, yes — but alive.


3) 1700s — Being squeezed from both sides

Threat: Partition between Siam and Vietnam
Danger: Extreme

  • Siam dominates the west.
  • Vietnam expands aggressively into the Mekong Delta.
  • Cambodian kings are installed and removed by foreign powers.

At this point Cambodia was a buffer state with almost no real power.

Why Cambodia survived:
Kings played both sides relentlessly — switching alliances whenever survival required it.


4) 1834–1845 — Vietnamese occupation

Threat: Cultural and political erasure
Danger: Possibly the closest Cambodia ever came to disappearing**

  • Vietnam directly controls Cambodia.
  • Cambodian administration dismantled.
  • Vietnamese officials attempt forced assimilation.
  • Khmer elites flee or are killed.

This was not just occupation — it was absorption in progress.

Why Cambodia survived:
Popular resistance + Siamese intervention forced Vietnam to withdraw.
If that war had ended differently, Cambodia likely would not exist today.


5) 1863 — The desperate choice

Threat: Permanent division between Siam and Vietnam
Danger: Final moment before extinction

By the mid-1800s:

  • Cambodia controlled almost nothing itself.
  • Siam held the west.
  • Vietnam dominated the east.
  • The king had no army strong enough to resist either.

The critical decision:
King Norodom accepted French protection.

This sacrificed independence — but saved the nation.

Without this move, Cambodia would almost certainly have been absorbed and erased within a generation.


6) 1975–1979 — Khmer Rouge

Threat: Physical destruction of the nation
Danger: Catastrophic

  • Nearly one quarter of the population dies.
  • Institutions destroyed.
  • Educated class eliminated.
  • The state collapses completely.

This wasn’t foreign conquest — it was self-destruction on a national scale.

Why Cambodia survived:
Vietnamese intervention ended the regime, and the people rebuilt from almost nothing.


The pattern you should notice

Every time Cambodia faced extinction, survival came from one of three things:

  1. Strategic retreat (leaving Angkor, moving capitals)
  2. Hard compromise (accepting vassalage or protection)
  3. Cultural endurance (Khmer identity outlasting political power)

Cambodia didn’t survive by winning wars.
It survived by making the least bad choice when all choices were bad.

That’s not a romantic story — but it’s a real one.

Why did the Khmer empire decline?

The Khmer Empire didn’t fall because of one single disaster.
It declined because several pressures hit at the same time, and together they were more than the empire could absorb.

Here’s the clear, honest breakdown.


Why the Khmer Empire declined

1) The empire grew too big to control

At its height, Angkor ruled:

  • Most of modern Cambodia
  • Parts of Thailand, Laos, and Vietnam

That’s impressive — but it created a problem:

The center became too far from the edges.

  • Communication was slow.
  • Local governors gained power and loyalty weakened.
  • Rebellions and breakaway regions became harder to stop.

The empire wasn’t defeated all at once — it slowly lost control from the outside in.


2) Environmental stress broke Angkor’s system

Angkor depended on one of the most complex water-management systems in the medieval world.

It worked brilliantly — until climate changed.

In the 1300s–1400s:

  • There were severe droughts, followed by massive floods.
  • Canals broke.
  • Reservoirs filled with sediment.
  • Rice production fell.

When food security weakens, everything weakens:

  • Army
  • Economy
  • Political stability

Angkor’s greatest strength became a liability.


3) Religious change weakened royal authority

For centuries, kings ruled as:

God-kings (Devaraja)

This system depended on:

  • Hindu state religion
  • Monumental temples
  • Absolute royal authority

Then Theravada Buddhism spread across the empire.

It changed society in a big way:

  • Less focus on divine kingship
  • More focus on monks, villages, and local communities
  • Power became decentralized

This was good for the people — but it weakened the state’s ability to mobilize huge resources for empire and war.


4) Strong enemies rose at the worst time

While the Khmer state was weakening:

  • Ayutthaya (Siam) was rising in the west
  • Vietnam was expanding in the east

Cambodia went from being:

the dominant power → to the buffer state

Angkor was attacked repeatedly, not just once.
The famous sack in 1431 was the final blow — not the beginning of the decline.


5) Internal conflict and unstable kingship

Late Angkor was full of:

  • Power struggles
  • Short reigns
  • Rival claimants
  • Civil wars

An empire can survive enemies.
It can survive droughts.
But when leadership is unstable at the same time, collapse accelerates.


The real answer in one sentence

The Khmer Empire declined because environmental collapse, religious change, political fragmentation, and foreign pressure all hit together, leaving Angkor unable to function as the center of a vast empire.


Important perspective

The empire didn’t “fail.”
It transformed.

The people didn’t disappear.
They became:

  • The Kingdom of Cambodia
  • A smaller state
  • A more flexible society

Empires fall.
Civilizations that adapt continue.

Cambodia is proof of that.

Horrors Causing Blindness

My mother-in-law, Srai Sim, lived through the horrors of the Khmer Rouge in Cambodia. I wrote her story here. When she told me her story, she mentioned how she began to lose her eyesight while toiling in the rice fields. She’s had trouble with her eyes ever since those days. I thought it strange and assumed it was/is due to the malnutrition and hard labor she endured under the Khmer Rouge soldiers.

I recently discovered the following article from the LA Times, titled Blinding Horrors: Cambodian Women’s Vision Loss Linked to Sights of Slaughter. I will share it in its entirety below…

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Eang Long cried for many days after the Khmer Rouge soldier beat her brother and his three children to death. She vividly recalls how the soldier threw the youngest child, a 3-month-old, against a tree until the baby died.

“My eyesight started to get terrible after I saw the tragedy,” Long said. “Because I was crying so hard and long, my eyes were red and started to swell up. Then I started to have problems with my eyesight.”

A decade later, Long, 65, who now lives in Long Beach, still has days when shadows–like silent phantoms of the past–obscure her vision. She says her bifocals do not always help and she fears her eyesight will get worse.

Long and dozens of other middle-aged Cambodian women are coping with a condition that some researchers have called “functional blindness”–blindness or visual problems caused by psychological factors.

Two researchers who have studied the condition say it is linked to post-war trauma stemming from the genocide by Communist leader Pol Pot and the Khmer Rouge in the late 1970s.

Gretchen Van Boemel, associate director of clinical electro-physiology at the Doheny Eye Institute in Los Angeles, says it was 1984 when she started to notice a disproportionate number of Cambodian women in the 40 to 60 age group who had the disorder.

“I talked about this with a friend who was involved in Southeast Asian affairs,” Van Boemel said, “and she described all the atrocities and killing fields in Cambodia.”

Armed with this information, Van Boemel contacted her friend and former college classmate Patricia Rozee-Koker, now a psychology professor at Cal State Long Beach. By 1985 the two researchers had located a group of 30 Cambodian women, ages 40 to 69, who volunteered to be in a study. All of the women had lived in Cambodia during the Pol Pot regime and later spent one to six years in a Thai refugee camp before being relocated to the United States.

Van Boemel said the purpose of the survey was to show that “a psychological overlay was causing the women’s eye problems, even if the brain was functioning normally.”

Each woman was interviewed and given an eye exam and a test to determine whether the visual system in the brain is functioning normally. Van Boemel said the test monitors brain waves as subjects look at checked patterns on a video monitor.

In each case, the test revealed normal visual acuity, often at the 20/20 or 20/40 level. These same women, however, when looking at an eye chart could barely see the top line of 20/200–the point of legal blindness. Other women had no light perception and could not detect light or dark shadows.

Rozee-Koker said most of the women’s functional blindness surfaced during the Pol Pot years. Personal interviews brought out repeated stories of forced labor, the murder of family and friends–often in their presence–beating and torture, starvation, a treacherous escape to Thailand and separation from family. She said the findings indicated that the longer a woman was bound to Khmer Rouge servitude or life in a refugee camp, the more her vision was impaired.

Reports Received Attention

Results of the study were presented at the 1986 American Psychological Assn. annual meeting in Washington. There was only one other paper about Cambodian refugee women and both reports received considerable attention. The paper, “The Psychological Effects of War Trauma and Abuse on Older Cambodian Refugee Women” is scheduled to appear in a coming issue of the journal, “Women and Therapy.”

The researchers found that the Cambodians do not always understand their condition and that many optometrists and ophthalmologists dismiss the vision loss as a case of “faking” or “malingering,” Van Boemel said.

As an example, Rozee-Koker pointed to a 1985 piece in the journal Ophthalmology. It described new immigrants who might be milking the welfare system with complaints of functional blindness. “That article was racist,” Rozee-Koker said. “But people believe it. It was very insensitive.”

Dr. Eric Nelson, a third-year resident at the UCLA School of Medicine, recently completed a preliminary study of Cambodians with functional blindness. “We found some patients who had been considered malingerers,” he said. “But our research proved this to be wrong.”

Unexplainable Problems

His findings were confirmed by Long Beach ophthalmologist Hector Sulit, who in the last five years has noticed a significant number of Cambodian women with unexplainable visual problems.

“I don’t think it has anything to do with their age, but because they lost family or children,” he said.

As more data about functional blindness in the Cambodian community became available, Rozee-Koker and Van Boemel decided to continue their study.

This fall they completed a 10-week study of 15 Long Beach Cambodian women. Each Saturday the women participated in a therapy or skills group for 90 minutes. The therapy group uncovered deep post-war trauma.

The most dramatic improvement took place in the skills group. As the women mastered such basic skills as taking a bus downtown, using a telephone and shopping, they felt a growing sense of empowerment over their lives.

Or as one Cambodian woman told Rozee-Koker: “When I am happy I see better.”

Improvement in Vision

“It was amazing to see the difference,” Rozee-Koker said. “From having to be guided by our arms into the elevator to the psychology building or holding themselves in a fetal position–to the last week when they were standing up straight. Many could smile and with some, their vision improved.”

For Chhou Chreng, 64, the sessions were an opportunity to learn how to dial 911 and to brush up on writing.

“I lost my vision in an accident in 1979,” she said. “Something fell on my head and then things were not clear.” Under Pol Pot she was forced to work in the rice fields for four years. Her husband, brother and many cousins died of starvation.

“Sometimes I will get a headache if I think about my sister in Cambodia,” she said. “Then I will get pain all over my body and my eyes will hurt.”

Both researchers, who are compiling their data, acknowledge that 10 weeks is not enough time to deal with these bouts of depression. Next year they hope to start a student intern program at Cal State Long Beach that will assist local Cambodian women.

Another agency, the nonprofit Community Rehabilitation Industries, also works with Cambodian women. Konthea Kang, a program coordinator at CRI, estimates that up to 20% to 30% of the dozens of Cambodian women she sees have had visual loss symptoms.

Older women, she said, have a more difficult time assimilating into American life styles. In Cambodia, most young people take care of their elderly relatives and parents. In rural areas, she said, women stay at home and raise families and many urban husbands also frown upon wives who work. When these women reach the United States, they are strongly encouraged by federal and state agencies to find a job. But in the workplace, they encounter yet another problem.

“When they can’t speak English, they don’t know what to do and get laid off,” Kang said. “After this they feel lost for several months.”

Tormented by Nightmares

As a counselor at the Asian Pacific Mental Health Center in Long Beach, the Rev. Kong Chhean said he tries to help his patients become more secure. The counselor and Buddhist monk has a caseload of about eight women with visual dysfunction symptoms. They are tormented by frequent nightmares about the Khmer Rouge and are afraid of attacks, even though they are half a globe away from the soldiers.

Although light is being shed on functional blindness, experts say that successful treatment is often tied to mental health care and that poses a problem in the Cambodian community.

Kung Chap, a vocational rehabilitation counselor at the Long Beach office of the California Department of Rehabilitation, said the concept of mental health care in Cambodia is negative. A mental health facility in Phnom Penh called Takhmao Hospital “looks like a jail,” he said. “The people there are labeled as crazy people. They would have been beaten and electric shock used on them.”

Cambodians, Chap said, would rather seek help from the family, a temple or a shaman with magic cures. They are slow to accept the American-style of counseling and therapy.

Rozee-Koker and Van Boemel have also found Cambodians to be afraid of agencies, hospitals and the university. On one occasion they made an appointment to interview a woman and her family. When they got to the house, the entire family had picked up and moved.

“We had evoked memories of the Khmer Rouge,” Rozee-Koker said. “To them it was a voice of authority. To their minds it sounded like Pol Pot.”

The refugees, Rozee-Koker said, will carry the scars of their experiences throughout their lives. “They do not want to see any more violence, any more pain. They have essentially closed their eyes to it.”

Or, as Chhou Chreng put, it, “When I feel happy my eyes are normal. When I think about Cambodia and my family I see flashes of light and dark.”

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Three Old Books About Cambodia

PP 1929
Phnom Penh – 1929 – Photo by Georges Portal

I enjoy finding old books about Cambodia online, especially history books.

Here are three public domain books I recently found. The first is about the ruins of Angkor written by P. Jeannerat De Beerski. The second is about how India was the main influence on early Cambodian culture, by Bijan Raj Chatterji. And the third is a short history of Cambodia, by Martin F. Herz. Enjoy….

Angkor – Ruins in Cambodia ~ 1924

Indian Cultural Influence in Cambodia ~ 1928

A Short History of Cambodia ~ 1958

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Three Articles About Cambodia and Thailand

Following are three well written 2003 articles by Matthew Z. Wheeler on Cambodia and Thailand from the website Institute of Current World Affairs.

You can find the original articles, along with others written by Wheeler, by clicking here.

I’ve uploaded PDF files of the Cambodia/Thailand articles below…

Thoughts from Bangkok on the Anti-Thai Riot in Phnom Penh

Cambodia’s 2003 Election

Appreciating Poipet

Related reading: Poipet Through the Ages; The Great Cambodian Exodus; From Siam to Suez ~ Bangkok; From Siam to Suez ~ Angkor