Reading Document: International Boundary of Cambodia -Siam
U.S Department of State
International Boundary Study
No. 40 (Revised) – November 23, 1966
Cambodia – Thailand
(Country Codes: CB-TH)
Office of the Geographer
Bureau of Intelligence and Research
Office of Research in Economics and Science
Bureau of Intelligence and Research
INTERNATIONAL BOUNDARY STUDY
TABLE OF CONTENTS
I. Boundary Brief……………………………………………………. 2
II. Geographical Background ………………………………… 2
A. Physical…………………………………………………………… 2
B. Historical …………………………………………………………. 4
C. Socio-economic………………………………………………. 5
III. Analysis of Boundary Alignment………………………. 6
IV. Treaties……………………………………………………………….. 7
A. Treaty between France & the Kingdom of
B. Treaty between France & the Kingdom of Siam… 7
C. Treaty between France & the Kingdom of Siam… 7
D. Convention for the regulation of certain difficulties…….. 8
E. Convention between France and Siam…………….. 8
F. Treaty between France and Siam…………………….. 8
G. Bangkok Protocol…………………………………………. 9
H. Bangkok Treaty between France ……………………..9
I. Tokyo Peace Convention………………………………….9
J. Washington Accord…………………………………………9
K. Judgment of the International Court………………….9
V. Summary…………………………………………………………….. 9
I. BOUNDARY BRIEF
The Cambodia–Thailand boundary stretches approximately 499 miles from the Gulf of Siam northward and then eastward to the Laos tri-point at the Col (pass) de Preah Chambot near the Mekong River. The boundary has been delimited by a series of agreements between France and Thailand during the period when Cambodia was under French control. Part of the boundary has been demarcated. For 326 miles, watersheds form the boundary while streams (130 miles) and straight line segments (43 miles) complete the total.
Since the Judgment of the International Court of Justice (ICJ) in 1962 acknowledging Cambodian sovereignty over the Preah Vihear Temple, no disputes over precise alignment have been raised by either state. Cambodia, however, in recent times has demanded that Thailand accept, at an international conference, the validity of the treaties with France delimiting the border and of the ICJ decision of 1962. While quite willing de facto to accept the status quo, Thailand has refused to do so by means of reference to the treaties with France, which she entered into under duress, or to the ICJ decision, concerning which she continues to maintain a rather vague reservation.
II. GEOGRAPHICAL BACKGROUND
The Cambodia–Thailand boundary transects three distinct physiographic regions:
• the Montes des Cardamomes in the southwest,
• the alluvial plain west of the Tonle Sap, and
• the Chaîne des Dangrek extending eastward to the Laos tripoint.
The Montes des Cardamomes and their continuation, the Banthat Range, constitute a complex mountain region with jagged summits and deeply eroded, almost precipitous valleys. The alignment of the ridges varies from northwest–southeast to north–south. Peaks generally average below 3,500 feet above sea level although certain isolated mountains attain heights of 5,000 feet. The basic rock is primarily sandstone although isolated granite batholiths loom over the adjacent lowlands as isolated massifs. In the extreme south, the elevations are much lower as the boundary follows a secondary ridge which forms the local watershed.
Northwest of Pailin, the boundary departs from the mountains to cross the alluvial lowland west of the Tonle Sap. For the first 50 miles, the lowland region is traversed by limestone ridges aligned generally north–south, parallel to the frontier. The elevation of the plain averages about 300 feet while the ridges tower approximately 1,200 to 1,500 feet above. Where the boundary joins the Huai Nam Sai, the true plain is attained. Its surface with an average elevation below 100 feet is almost completely level except for a few isolated, rounded hills which break the surface. The plain extends northward for an additional 55 miles before the third feature, the Dangrek, is encountered.
The Chaîne de Dangrek forms a narrow range of eroded sandstone hills. It presents a steep escarpment south to the Cambodian plain and gentler slopes to the north, the Thai Khorat (Nokor Reach). The mountain area is only 20 to 25 miles wide although finger-like ridges project perpendicularly north and south from the main axis. Although the maximum elevation is approximately 2,300 feet, the Dangrek’s average is approximately 1,600feet.
The climate of the frontier region reflects the seasonal migration of the monsoons which determine both the rainfall and temperature patterns of Southeast Asia. The rainy, southeastern monsoon reaches the area in May and remains until mid-October. During this season, most of the annual precipitation is registered. A typical station, with a total annual precipitation of 85 inches, will receive about 70 inches in this period. In October, the monsoon shifts to the northwest bringing with it the dry season. While the change is not abrupt, it is rather marked. The total annual rainfall varies little from year to year.
Great variations, however, do occur as a result of elevation and exposure. The maximum rainfall is registered in the Cardamomes (c. 200 inches) and the minimum in the plain (c. 55 inches). Because of winter cyclonic activity no month of the year is totally without precipitation. A typical lowland station has an average annual temperature of approximately 82° F. Maximum monthly averages register around 90° F. while minimums are 75° F. The daily range in temperature approximately equals the annual range. The coolest month is January and the hottest is April, just before the monsoon’s arrival. While data are lacking for the highlands, temperatures are lower as a consequence of the increased elevations.
Approximately 50 percent of both Cambodia and Thailand are covered with forests.
The frontier regions, being essentially isolated from the main areas of settlement in the two states, have an even higher percentage. The densest stands are found in the mountains along the Gulf of Siam which are exposed to the full force of the southeastern monsoon. Here high precipitation, tropical temperature, and adequate soils have combined to produce rich equatorial rain forests. Major species are pine, ebony, mahogany (red and dark), and rose wood. Teak is not indigenous to the area although it is grown elsewhere in the two countries. Isolation from major markets has limited the exploitation of valuable woods.
Further to the north, where population density is greater and precipitation lower, the forests are more open and often represent secondary growth. “Slash and burn” agriculture by the hill tribes and commercial exploitation have combined to reduce the extent and quality of the forests. In external appearance the secondary, monsoon forest resembles the rain forest. However, the valuable, slower growing hardwoods are almost totally lacking. Except in areas of pronounced drought, the forests are evergreen, multilayered, and easily penetrated. Single stands of trees rarely dominate a region; rather multiple species abound. Undergrowth is rare, although tough, coarse grasses are common in more open areas.
Civilization in Southeast Asia is essentially riverine. The two great cultural developments in the region around the Cambodian–Thailand border have been that of the Thai in the Chao Phraya (Menam) valley to the west and the Khmer in the Mekong– Tonle Sap depression to the east. The Khmer empire emerged first. Coming from the northeast, the Khmer and related Chams settled in the lower Mekong valley about the first century. By peaceful means, these people became Hinduized in religion, culture, and social structure. The isolated communities gradually coalesced into the state which commanded much of Southeast Asia. By the 9th century, the Khmer empire, centered on the city of Angkor Wat, extended eastward to the Annamite Chain, westward to the Gulf of Siam and southward to the delta of the Mekong. Modern-day Laos was under Cambodian suzerainty if not sovereignty. The Khmer state reached a zenith of power
from the 9th through the 13th centuries.
The first Thai Kingdom known to history was Nan-Chao, located near what is now Yunnan, which resisted the southward thrust of successive Chinese dynasties from roughly the 7th through the 12th centuries. However, it was shattered by the Mongol conquest in the 13th century. This latter event speeded a southward movement of Thai peoples that had been going on gradually for several centuries. Minor Thai kingdoms appear in what is now northern Thailand as early as the 11th century. In the 13th century, the Kingdom of Sukothai, although its capital was in the north, claimed control of much of the central and south of present-day Thailand, and frequently clashed with the Khmer. In 1350 the Kingdom of Ayudhya, forerunner of the present Thai state, was founded on the lower reaches of the Chao Phraya river. The present capital was founded in 1782 by the first king of the present (Chakri) dynasty. In their southward movement, the Thai displaced and, to a degree, assimilated the Mon people, and drove out the representatives of the Khmer. Conflicts became sharper as the Thai pushed their control eastward, even raiding several times the ancient capital of Angkor Wat, which the Khmer abandoned to the jungle in the 15th century. Thai pressure on the weakened Khmer from the west was matched by Vietnamese pressure on the north and east. By the mid-19th century the Thai and Vietnamese exercised joint protection over present-day Cambodia through kings which they hand-picked. European influence was first felt in the 16th century. First Portuguese and later Dutch traders obtained concessions to engage in commerce. French influence originally came into the region through the efforts of missionaries. In the latter part of the 17th century, commercial ventures supplemented religious activities. French influence waxed powerful and then waned sharply during the next century. However, by the middle of the 19th century, France, determined to obtain a share of Chinese trade, made a concerted effort to gain a foothold in the Indo-Chinese peninsula. Cochin-China became a colony; Cambodia and Annam followed as protectorates. In the meantime, British influence had spread from India into the Burmese lands of the lower Irriwaddy.
As the French and British both began occupying territories also claimed by the Thai kingdom, the possibility of a Franco–British clash arose. After a serious crisis in 1893, the British and French, in 1896, came to an agreement that neither would occupy the Chao Phraya valley. This left Thailand’s northeast still vulnerable, and in fact the French did advance further at Thailand’s expense there. They annexed a part of what is now Cambodia above Tonle Sap (and also Sayaboury province of what is now Laos) in 1904, and added Siem Reap, Battambang, and Sisophon of what is now Cambodia in 1907. However, thanks in part to the Anglo–French treaty of 1896 and in part to the skillful diplomacy and the virtual revolution of modernization of the Thai state carried out by the Thai King in the late 19th century, Thailand survived, the only state in South and Southeast Asia to maintain its independence throughout the period.
Some influential elements in Thailand continued to look upon the territories lost to the French, especially that in 1904 and 1907, as irredenta and, after the fall of France in 1940, the Thai attacked the French armies in the area with a view to recovering the territory. After several clashes had taken place, the Japanese offered to arbitrate and induced the French and the Thai to sign the Tokyo Peace Convention of May 9, 1941.
It inter alia returned to Thailand the Cambodian territories taken by the French in 1907. After Germany’s defeat, the French demanded the return of these territories and following a long and bitter negotiation this was provided for in the Washington Accord of November 17, 1946.
After Cambodia regained its independence, a border problem came to light again involving a “lost” Khmer temple, Preah Vihear, situated on the edge of the Dangrek escarpment. Thai police forces had occupied the temple and began to perform administrative actions. Cambodia protested but did not force the issue. Finally, in 1959, the question of sovereignty was submitted to the International Court of Justice.
Thailand’s position was that the temple was north of the watershed line specified as the Dangrek boundary by the 1904 and 1907 treaties. Cambodia based its case on the delimitation commission map which showed that the boundary in places deviated from the watershed; Preah Vihear was only one instance. In 1962, the Court ruled that the map of the eastern Dangrek range was valid and the temple was Cambodian. Although pleased by the favorable ICJ decision, Cambodia has felt somewhat frustrated over the fact that the Thai, while accepting the decision de facto, have maintained a rather vague reservation with respect to it. Cambodia has recently called for an international conference on the “neutrality and territorial integrity” of Cambodia to seek inter alia formal Thai acceptance of the validity of the Thai–French treaties which delimit the boundary (which the Thai maintain were entered into under duress) and of the 1962 decision of the ICJ. While expressing willingness to agree to some formulation showing their acceptance of the status quo, the Thai have not been willing to express it in this way. Thus while there is no active boundary dispute between the two countries at the moment, the history of such disputes is an important factor in the extremely bad Thai– Cambodian relations of the present.
The immediate frontier region is not of great economic or social importance to either state. Everywhere the population density is less than 10 inhabitants per square kilometer, and in the uplands the average is less than one per square kilometer. In the extreme south, the watershed boundary in the coastal range is an ethno-linguistic divide as well; Thai inhabit the region to the west and Khmer that to the east. However, small and scattered elements of Mon-Khmer occupy isolated areas in the rugged mountains. The most widespread of these tribes are the Pear. Unlike the hill tribes of the Annamese highlands, the Mon-Khmer of the west have been prone to accept at least the trappings of the modern Cambodian. As a consequence, they are tending to disappear as a separate ethnic entity.
To the west of Battambang, Khmer people extend across the frontier into the Thai changwats of Chanthaburi and southern Prachin Buri. At the northern end of the north– south sector of the frontier, the boundary again is an ethno linguistic divide.
In the Dangrek, however, the inhabitants are primarily a Mon-Khmer people known as the Kui. Occasionally Thai (Lao) or Khmer villages are found interspersed among them. The Kui, like the Pear, are fast becoming acculturated into Thai or Khmer patterns. Essentially Mountain or Tribal Khmer, they speak a language closely associated with modern Cambodian.
Routes across the frontier are rare. The principal area of transit is in the lowland west of Sisophon. Here, the Phnom Penh–Bangkok railroad and surfaced road serve as the main arteries between the two nations. Elsewhere, national routes lead up to but not across the frontier.
III. ANALYSIS OF BOUNDARY ALIGNMENT
Starting in the south on the Koh Kong peninsula, the Cambodia–Thailand boundary follows the watershed of the coastal range of the Cardamomes northward for a distance of 103 miles through a heavily forested region. West of the Pailin, the boundary joins the Stung Pailin (and a tributary stream) for 12 miles. Leaving the stream the boundary extends northward for two miles to join the headwaters of a right-bank tributary (O Taker) of the Stung Mongkol Borey. These two streams are the boundary for 12.5 miles. West of Ben O Chieng, the boundary passes westward and northward by a series of straight lines (total length, 10 miles) to boundary pillar 52 on the Stung O Dar. The boundary then follows the river upstream for 18 miles to its source on (mount)
Khbal Thbal. A short segment of 1.3 miles then brings the boundary to the source of the Nam Sai which is followed to its confluence with the Stung Bang Haut (Pahout) (Sisophon). The latter forms the boundary westward to Poipet. The total of the two rivers measures 76.4 miles.
From Poipet, a straight line northeastward for 15 miles serves as the boundary to the Stung Kone Kriol. Crossing the river, the boundary for 2 miles coincides with a tributary of this river. Again, as a series of geometric lines, the boundary extends northeastward and northward for 18.7 miles to the Stung O Say which is utilized downstream to the Stung Svay Chek. Following this upstream to the Stung O Pao, the boundary then coincides with this latter stream for 15.5 miles to its source in the Dangrek.
Turning eastward, the boundary, in the main, coincides with the watershed along with Dangrek escarpment to the Col de Preah Chambot, the tri-point with Laos. Certain modifications in the Dangrek boundary were made by the delimitation commission. While most of the departures from the watershed are very minor, one involved the temple of Preah Vihear which led to the Cambodia–Thai dispute. The International Court of Justice ruled that the map of the delimitation commission, even though it was made only by the French section, had by Thai acceptance become a valid document in the determination of the boundary. While the decision applied specifically to the temple case, it may be extended by analogy to the other maps. Cambodia considers the commission maps to be the official depiction of the boundary.
The boundary between Thailand and Cambodia has been delimited by international agreement and, in part, has been demarcated. Wooden pillars were placed along the boundary south of the Dangrek, apparently by the original commission. These soon rotted out and after World War I were replaced by more permanent monuments. Both Thai and Cambodian maps show these pillars although there is no consistency in the numbering of them. About 75 appear to have been established. The pertinent delimitation treaties are listed below:
A. Treaty between France and the Kingdom of Cambodia signed on August 11, 1863, with ratifications exchanged on April 14, 1864. (BFSP 57:739)
By the terms of Article I, the French Emperor extended protection to the King of Cambodia.
B. Treaty between France and the Kingdom of Siam over the regulation of the
political situation and the limits of Cambodia, signed on July 15, 1867, with
ratifications exchanged on November 24, 1867. (Ibid. 57:1340)
Siam in Article I recognized French protection over Cambodia.
By Article IV Battambang and Angkor (Nakhou Siemrap) provinces were ceded to Siam.
A delimitation commission was also created.
C. Treaty between France and the Kingdom of Siam, signed on October 3, 1893,
with ratifications exchanged February 3, 1894. (Ibid. 87:187)
The territorial provisions of this treaty affected Laos only but Article 2 restricted navigation on the Tonle Sap, then a border lake.
D. Convention for the regulation of certain difficulties in delimitation…between
France and Siam signed on October 7, 1902. (Code de la Nationalite francaise,
Tome 2eme–Partie documentaire, 1946, p. 863.)
The Convention was never ratified and was soon replaced by E. below. However, its provisions first established the Dangrek as a boundary.
E. Convention between France and Siam for the regulation of certain
difficulties… signed February 13, 1904, with ratifications exchanged on December
9, 1904. (BFSP 97:961) with Protocol supplementing articles 1 and 2 signed June
The boundary was defined as the left bank of the Great Lake to the mouth of the Stung Roluos, then due east to the junction with the Prek Kompong Tiam which was followed north to the Dangrek. Then the boundary became the Dangrek watershed to the Mekong. The delimitation commission created by this convention began a series of maps which were eventually published and served as a documentation in the Preah Vihear case. Before the commission could complete its work, however, a new treaty (below) superseded much of its labors.
The supplemental Protocol of June 29, 1904, defined the boundary west of the Great Lake (Tonle Sap) as the watershed line separating the basin of the lake from the basin of the Stung Krevanh (Pursat River) to the mountains which form its source. Then it followed the river Barain (Huay Reng) to the Tungyai and then to the Kratt estuary. Following this to the confluence with the Klong-Dja the boundary proceeded upstream along this water course to its source on (mount) Kaomai-See. From this point, the boundary followed the chain of mountains to (mount) Kao-Knun and from here a second chain to the extremity of Cape Lem-Ling.
F. Treaty between France and Siam with a protocol concerning the delimitation
of frontiers, signed on March 23, 1907. (1907 U.S. Foreign Relations 2:1003; U.K.
Cmd. 3578 (1907).
By the terms of Article I, Siam ceded the territories of Battambang, Siemreap and Sisophon in exchange (Article II) for Dan-Sai and Krat (Trat). This action nullified the 1904 delimitation in the northwest and west. The attached protocol redefined the new boundary as a point (on the shore) facing the highest point on the island of Koh-Kut northeast to the summit of Phnom-Krevanh coinciding with the line forming the western watershed of the Klong-Kopo, the entire basin of which fell to Indochina. Continuing northward along the watershed to Phnom-Thom, the boundary then joined the western frontier of the province of Battambang which was followed to the river Nam-Sai. The Nam-Sai formed the frontier to its confluence with the Sisophon which then became the line to a point 10 kilometers below (downstream) from the city of Aranh. Then the boundary was delimited as a straight line to a point situated on the Dangrek between the passes of Chong-Ta-Koh and Chong-Sa Reck. Then the watershed of the Dangrek
became the boundary.
Finally, the commission of delimitation was given authority to determine the precise trace on the ground and to substitute natural lines (i.e., ridges, streams, etc.) for the convention lines, a process which has obviously been followed.
G. Bangkok Protocol signed February 14, 1925, and Convention signed August 25,
1926 (69 LNTS 315 No. 1613 (1927/28).
These agreements modified the Laos boundary in the Mekong but confirmed the earlier
Cambodia–Thai boundary delimitations without change.
H. Bangkok Treaty between France and Thailand signed December 7, 1937.
The same situation prevails as in G. above concerning the Cambodia–Thailand frontier.
I. Tokyo Peace Convention signed May 9, 1941.
The pre-1900 boundary between Laos and Cambodia and Thailand was, for the most part, restored.
J. Washington Accord signed November 17, 1946 (Code de la Nationalite francaise
op. cit. p. 809).
This Accord annulled the Tokyo Convention and returned the prewar boundary to force.
K. Judgment of the International Court of Justice rendered on June 15, 1962 -
“Case concerning the Temple of Preah Vihear (Cambodia v. Thailand)”
After examining the evidence submitted by both states, the Court rules that the map of the eastern Dangrek created by the 1904 and 1907 delimitation commissions had validity and the temple was in Cambodia.
Although no questions have been raised as to the precise alignment of the boundary since the ICJ settlement of 1962, the history of this boundary nevertheless contributes to the present very bad relations between the two states. There are occasional “border incidents”, usually involving smuggling or other crime, but if relations were otherwise good, these difficulties could be settled amicably.
Map compilation of the boundary on official U.S. productions should adhere to the maps of the original delimitation commissions. These series are:
Commission de Délimitation de la Frontière entre l’Indochine et le Siam, 1:200,000
Secteur No. 1 1908–8
Secteur No. 2 1908–9
Secteur No. 3 1908–9
Secteur No. 4 1907–8
Secteur No. 5 1907–8
Commission de Délimitation entre l’Indochine et le Siam, 1:200,000
(Sheet) Khong 1906–7
Note: The remaining sheets of this series for Cambodia are replaced by the five listed above.
The remainder shows the superseded 1904 frontier.
A comparison has been made between these maps and the series Carte de l’Indochine
1:100,000 published by the French Service Géographique de l’Indochine and
subsequently by the independent states of former Indochina. Except for minor changes
in geographic positions, the boundary is identical with one exception. Northwest of Sisophon, the delimitation commission maps show a single geometric line extending directly from the Stung Kone Kriol (Kriel) to (mount) Phnom Chatt. The modern French map shows three line segments positioned generally to the east. However, the relationships between places and the boundary are identical. Moreover, modern Thai maps also show the boundary line in three segments. We conclude that the modern map shows positions more correctly and hence is an accurate representation of the earlier line.
Consequently, the 1:100,000 map series, which has a grid system and is hence more useful than the commission maps, may be used as a compilation source.