Looking for the roots of the current Thai-Cambodian conflict only in 19th-20th century border drawing is to ignore centuries of Cambodian history. Modern disputes around Preah Vihear, the Dangrek escarpment, and “Inner Cambodia” lie on top of a much older story of Siamese expansion into Khmer lands, beginning already in the last centuries of Angkor and intensifying under Ayutthaya and the early Bangkok kings.
Angkor under pressure from rising Siam
From the mid‑14th century, as the classical Khmer Empire weakened, Tai polities such as Sukhothai and especially Ayutthaya emerged as powerful rivals, taking over former Khmer dependencies like Lavo and pushing the political frontier closer to Angkor.
Studies of “Siamese attacks on Angkor before 1430” argue that instead of a single sudden conquest, Angkor faced a sequence of raids and campaigns from Ayutthaya, culminating in—but not beginning with—the famous siege of 1430–1431.
The fall of Angkor: conquest and cultural appropriation
In 1430–1431, Ayutthayan forces under King Borommarachathirat II besieged Angkor for months and finally stormed it, carrying off population, treasure, and ritual objects in an episode remembered as the Fall of Angkor.
After this, the Khmer royal center shifted south toward the Tonle Sap and the emerging Phnom Penh region, while Ayutthaya adopted and reworked Khmer court architecture, ceremonial styles, and religious art—creating a paradoxical relationship in which the conqueror both admired and cannibalized Angkorian culture.
Longvek 1594: Cambodia’s “second fall”
A new capital at Longvek in the 16th century represented an attempt at Khmer recovery, but tensions with Ayutthaya remained high.
During the Siamese–Cambodian War of 1591–1594, King Naresuan returned to Cambodia with a large army and, after a prolonged siege, took Longvek on 3 January 1594; accounts emphasize massive deportations—tens of thousands of Cambodians, including Prince Soryopor, were carried off to Ayutthaya—and treat the fall of Longvek as a decisive downturn in Cambodia’s fortunes.
Deportations, humiliation, and enduring grievances
Descriptions of Naresuan’s victory in Thai‑language and modern popular narratives highlight ritualized humiliation of the Khmer ruler and population, reinforcing a memory on the Cambodian side of being treated as a conquered, exploitable people.
For subsequent centuries, Cambodia functioned intermittently as a reservoir of labor and a field of war for Siam, with cyclical campaigns bringing new waves of captives into Siamese territory and leaving deep demographic scars on the Khmer countryside.
Inner Cambodia: Battambang, Siem Reap and Angkor under Siam
By the late 18th century, Siam had moved from episodic invasion to permanent control over large parts of north‑western Cambodia.
In 1794, in the context of placing Prince Ang Eng on the throne, Siam appropriated Battambang and Siem Reap—including the ruins of Angkor—forming the region later known as “Inner Cambodia”; these provinces were governed directly from Bangkok until they were returned to French‑ruled Cambodia in 1907.
Ang Chan II and dual vassalage
When Ang Eng died, his son Ang Chan II eventually acceded under Siamese protection: he was recognized and crowned in Bangkok in the early 19th century and paid regular tribute to the Siamese court.
Facing internal opposition led by his brother Ang Snguon and pressure from Bangkok, Ang Chan II turned to Emperor Gia Long of Vietnam in 1811; Vietnamese forces restored him, shifted the capital to Phnom Penh under a Vietnamese‑built citadel, and left Cambodia effectively divided—Siam entrenched in the west (Inner Cambodia), Vietnam dominant in the east—while Ang Chan II sent tribute to both courts.
A kingdom hollowed out before the French maps
By the mid‑19th century, Cambodia had endured the sack of Angkor, the fall of Longvek, repeated deportations, and the partition of its territory between Siam and Vietnam; scholars describe the kingdom as a “pawn” in a regional power struggle rather than a fully sovereign actor.
Puangthong Pawakapan’s detailed study of Siamese interventions from 1767 to 1851 concludes that warfare, exploitation of manpower, and control of trade routes so weakened Cambodia’s demographic and economic base that it was no longer a viable political entity—setting the stage for French protectorate offers and later border negotiations.
Colonial treaties on an older battlefield
When the French protectorate was proclaimed in 1863 and when the Franco–Siamese treaties of 1904 and 1907 finally fixed the modern border, these agreements did not create the Thai-Cambodian rivalry out of nothing.
They instead froze, in legal form, a frontier that had already shifted repeatedly through conquest—from Angkor’s fall, to Longvek’s sack, to the century‑long Siamese administration of Battambang and Siem Reap—ensuring that temples like Angkor Wat and Preah Vihear would be read simultaneously as Khmer heritage and as former Siamese possessions.
From Angkor to Preah Vihear: why the longue durée matters
Today’s confrontations around Preah Vihear, Ta Krabey, Ta Muen Thom, and the Dangrek hills take place in a landscape layered with memories of Angkor’s siege, Longvek’s destruction, the depopulation of “Inner Cambodia”, and the double vassalage under Ang Chan II.
To speak only of “colonial borders” is therefore to erase the older Khmer experience of invasion, labor conscription, and cultural dispossession, and to misunderstand why many Cambodians see the Thai-Cambodian conflict as part of a centuries‑long story rather than a problem of 20th‑century cartography.
For Angkor and its fall: David Chandler, A History of Cambodia (chapters on the late Angkorian period and the move to the south); Lawrence Briggs, “Siamese Attacks on Angkor before 1430”, and recent summaries on Angkor Database.
For Longvek and the 16th‑century wars: entries on the Siamese-Cambodian War (1591–1594) and the Fall of Longvek, plus Nhim Sotheavin’s article “Considerations Regarding the Fall of Longvek” in Udaya.
For the Bangkok era and Ang Chan II: Puangthong Rungswasdisab, War and Trade: Siamese Interventions in Cambodia, 1767–1851; David Chandler’s work on Tai and Vietnamese hegemony; and biographical notes on Ang Chan II from Britannica and specialist Cambodian history sites.
For colonial borders and modern disputes: analyses of the Franco-Siamese treaties and “Inner Cambodia”, along with recent articles on the Thai-Cambodian border conflict and the Preah Vihear case in international law and regional studies journals.
