The earliest traces of armed conflict in the territory that constitutes modern Cambodia date to the Iron Age settlement of Phum Snay in north-western Cambodia.
Sources on Funan's military structure are rare. Funan represents the oldest known regional political entity, formed by the unification of local principalities. Whether these events must be categorized as conflict remains unclear More information is available for Funan's successor state - Chenla, which has been characterized as distinctly bellicose as it was established by the military subjugation of Funan. Chenla's early aristocrats heralded authority by public display of their noble genealogies carved onto stone stelae all over Indochina. Later, rulers increasingly embraced the concept of divine Hindu kingship.
The Khmer Empire's territory and integrity was maintained through the Royal Army, personally commanded by the king. Records exist for regular conflict with the kingdom's neighbors, Champa in particular, as the empire effectively controlled Mainland South-east Asia by the 12th century. Nonetheless, the Khmer kingdom suffered a number of serious defeats, such as the Cham invasion and sack of Angkor in 1177. Khmer military supremacy declined by the early 14th century. Since the rise of the Siam Sukhothai Kingdom and later the Ayutthaya Kingdom the empire experienced a series of military setbacks, unable to repel repeated attacks, that eventually caused its collapse followed by the Post-Angkor Period.
The period of decline and stagnation (around 1450 to 1863) nearly ended the Khmer aristocrat's royal dynastic sovereignty and unity of the Khmer people as the result of prolonged encroachments by its neighbours Vietnam and Thailand. In 1863 the Cambodian king acquiesced in the establishment of a French protectorate over his country to prevent its imminent incorporation into Vietnam in the east and the loss of its western provinces to Thailand.
No centrally organized military actions took place during the French protectorate, although notable was an 1883/84 nationwide revolt "which saw thousands of French troops do battle with shadowy bands of Cambodian guerrilla insurgents throughout the countryside". Several local uprisings are accounted for, which caused considerable problems for the colonial authorities. However, mainly reactions to French tax rulings and other perceived legislative injustices and without clear political objective, these endeavours had no decisive consequences. French colonial troops engaged in several conflicts with Thailand and suppressed revolts in Vietnam and Laos.
The Japanese incursion and 1945 coup d'état initiated a decade of political and ethnic re-emancipation of Cambodia, brought about without large-scale military action. Since Cambodia's independence in 1954 the country was to be the stage for a series of proxy wars of the cold war powers, foreign incursions and civil wars, that only effectively ended with the UN Mandate in the early 1990s.
Early history
The earliest traces of armed and violent conflict have been found at the Iron Age settlement of Phum Snay in north-western Cambodia. A 2010 examination of skeletal material from the site's burials revealed an exceptionally high number of injuries, especially to the head, likely to have been caused by interpersonal violence. The graves contained a quantity of swords, other offensive weapons used in conflicts. The presence of shoulder decorations and armour suggests a distinct military and/or clan culture, that has, according to some authors similarities with the Thai Iron Age sites such as Noen U-Loke and Ban Non Wat.
Funan is only known from Chinese sources, which according to most modern historians are doubtful. The polity was fully established around the 1st century CE and consisted of "walled political centers", which implies a desire to be prepared for some kind of conflict and to be protected from attacks. Some authors also argue that Funan was "expansionist" and might have maintained a sizeable navy that conquered regional coastal settlement centers. However, the Champasak territory of Laos was aggressively incorporated, although this might have taken place after the establishment of Funan's successor state - Chenla.
Some modern historians such as M. Vickery have redirected research and focus on archaeology, local genealogy and examined the suspicious size fluctuations and curious shifts of central power that characterized Chenla. Consequently, they argue, that Funan and Chenla, in particular, are terms not to be taken too seriously and accept greater political and military division among the elite. As contemporary Chinese sources on Chenla only provide factual reference points, such as the claim that by 616/617 CE the kingdom of Chenla is the region's new souvereign and...the conqueror of Funan. In 802 CE a powerful and contentious ruling dynasty united sizable territories and established the Khmer Empire.
Khmer Empire
Bas-relief in galleries of the Angkor complex in Siem Reap elaborately depict the empire's land and naval forces and conquests of the period (802 to 1431), as it extended its dominions to encompass most of Indochina. Hindu warrior kings, who actually led troops in battle, did not customarily maintain standing armies but raised troops as necessity required . Historian David P. Chandler has described the relationship between the monarch and the military:
Though the king, who led his country into battle, sometimes engaged his chief enemy in single combat, Khmer military strength rested on the junior officers, the captains of militia. These men commanded the loyalty of peasant groups in their particular locality. If the king conquered a region, a new captain of militia would be enrolled and put under an oath of allegiance. The captains were simply headmen of the outlying regions, but their connection with the king enhanced their status. In time of war they were expected to conscript the peasants in their district and to lead them to Angkor to join the Khmer army. If the captains disobeyed the king they were put to death. The vast majority of the Khmer population were of the farmer-builder-soldier class.
Little is known conclusively about warfare during imperial Cambodia, but much has been assumed from the environment or deduced from epigraphic and sculptural evidence. The army was made up of peasant levies, and because the society relied on rice cultivation, Khmer military campaigns were probably confined to the dry season when peasant-soldiers could be spared from the rice fields. Battles were fought on hard-baked plains from which the paddy (or rice) had been harvested. Tactics were uncomplicated. The Khmer engaged their foes in pitched frontal assaults, while trying to keep the sun at their backs. War elephants were widely employed, for both tactical and logistical purposes. Late in the Khmer Empire, the ballista (a kind of catapult, often shaped like a giant crossbow) took its place in regional warfare. It probably was introduced to the Cambodians by Cham mercenaries, who had copied it earlier from Chinese models.
Throughout the empire’s history, the court was repeatedly concerned with quelling rebellions initiated by ambitious nobles trying to achieve independence, or fighting conspiracies against the king. This was particularly true each time a king died, as successions were usually contested.
The Khmer Empire's principal adversaries were the Cham of the powerful kingdom of Champa in modern central Vietnam and to a lesser extent the Pagan Kingdom to the west. Warfare was endemic and military campaigns occurred continuously. The Chams attacked by land in 1177 and again by water in 1178, sacked Angkor twice. The empire quickly recovered, capable to strike back, as it was the case in 1181 with the invasion of the Cham city-state of Vijaya. In 1181 a young nobleman who was shortly to become Jayavarman VII, emerged as one of the great Khmer kings, raised an army and defeated the Chams in a naval battle. After Champa's decline began the rise of Cambodia's new enemies, the Siamese and the Vietnamese.
Post-Angkor Period As some scholars assert that the decline of the Khmer Empire was, among other causes, mainly precipitated by the drain on its economy. Dynastic rivalries and slave rebellions are also considered to have affected the demise of the empire.
Military setbacks Although a number of sources, such as the Cambodian Royal Chronicles and the Royal chronicles of Ayutthaya contain recordings of military expeditions and raids with associated dates and the names of sovereigns and warlords, several influential scholars, such as David Chandler and Michael Vickery doubt the accuracy and reliability of these texts. Other authors criticise this rigid "overall assessment", though.
David Chandler states in A Global Encyclopedia of Historical Writing, Volume 2: "Michael Vickery has argued that Cambodian chronicles, including this one, that treat events earlier than 1550 cannot be verified, and were often copied from Thai chronicles about Thailand..." Linguist Jean-Michel Filippi concludes: "The chronology of Cambodian history itself is more a chrono-ideology with a pivotal role offered to Angkor." Similarities apply to Thai chronological records, with the notable example of the Ramkhamhaeng controversy.
According to the Siamese Royal chronicles of Paramanuchitchinorot, clashes occurred in 1350, around 1380, 1418 and 1431.
"In 1350/51; probably April 1350 King Ramadhipati had his son Ramesvara attack the capital of the King of the Kambujas (Angkor) and had Paramaraja (Pha-ngua) of Suphanburi advance to support him. The Kambuja capital was taken and many families were removed to the capital Ayudhya. At that time, [around 1380] the ruler of Kambuja came to attack Chonburi, to carry away families from the provinces eastwards to Chanthaburi, amounting to about six or seven thousand persons who returned [with the Cambodian armies] to Kambuja. So the King attacked Kambuja and, having captured it, returned to the capitol."[sic]
Colonial Cambodia
Insurrections
Following negotiations by Cambodian King Ang Duong and Napoleon III for protection from Vietnam conquest and land loss by Thailand, a delegation of French naval officers concluded the French protectorate with King Norodom (1859–1904).The intervention of colonial France prevented further erosion of national and cultural integrity of Cambodia and ended territory loss.
Heavy taxation, institutionalisation of land ownership, reforms, that weakened the privileged status of the Cambodian elite, as well as resentment against foreign domination, were the causes of intermittent rebellions that marked the colonial period. Revolts erupted in 1866, in 1870 and 1883/84 that attracted considerable support in the countryside, easily quelled by the French, who created discord among the Khmer forces. Sisowath, Norodom's half brother led his troops into combat alongside the French who nourished his ambitions for the royal crown. Quelling the rebellion took one and one-half years, and it tied down some 4,000 French and Vietnamese troops that had been brought in from Cochinchina.
Ethnic Khmer colonial forces
The colonial military forces in Cambodia, tasked to quell potential insurrections, consisted of a light infantry battalion (Bataillon tirailleurs cambodgiens) and a national constabulary (Garde nationale, also called Garde indigène).
The light infantry battalion, a Khmer unit with French officers, was part of a larger force, the third brigade, which had responsibility for Cambodia and for Cochinchina. In addition to the Cambodian battalion, the brigade was composed of French colonial and Vietnamese light infantry regiments and support elements. The brigade, headquartered in Saigon, was ultimately responsible to a supreme military command for Indochina located in Hanoi.