Cambodia is country in Southeast Asia, can be traced back to at least the 5th millennium BC. Detailed records of a political structure on the territory of what is now Cambodia first appear in Chinese annals in reference to Funan, a polity that encompassed the southernmost part of the Indochinese peninsula during the 1st to 6th centuries. Centered at the lower Mekong, Funan is noted as the oldest regional Hindu culture, which suggests prolonged socio-economic interaction with maritime trading partners of the Indosphere in the west. By the 6th century a civilisation, called Chenla or Zhenla in Chinese annals, firmly replaced Funan, as it controlled larger, more undulating areas of Indochina and maintained more than a singular centre of power.

The Khmer Empire was established by the early 9th century. Sources refer here to a mythical initiation and consecration ceremony to claim political legitimacy by founder Jayavarman II at Mount Kulen (Mount Mahendra) in 802 C.E. A succession of powerful sovereigns, continuing the Hindu devaraja cult tradition, reigned over the classical era of Khmer civilization until the 11th century. A new dynasty of provincial origin introduced Buddhism, which according to some scholars resulted in royal religious discontinuities and general decline. The royal chronology ends in the 14th century. Great achievements in administration, agriculture, architecture, hydrology, logistics, urban planning and the arts are testimony to a creative and progressive civilisation - in its complexity a cornerstone of Southeast Asian cultural legacy.
The decline continued through a transitional period of approximately 100 years followed by the Middle Period of Cambodian history, also called the Dark ages of Cambodia, beginning in the mid15th century. Although the Hindu cults had by then been all but replaced, the monument sites at the old capital remained an important spiritual centre. Yet since the mid15th century the core population steadily moved to the east and - with brief exceptions - settled at the confluence of the Mekong and Tonle Sap rivers at Chaktomuk, Longvek and Oudong.

Maritime trade was the basis for a very prosperous 16th century. But, as a result foreigners - Muslim Malays and Cham, Christian European adventurers and missionaries - increasingly disturbed and influenced government affairs. Ambiguous fortunes, a robust economy on the one hand and a disturbed culture and compromised royalty on the other were constant features of the Longvek era.
By the 15th century, the Khmers' traditional neighbours, the Mon people in the west and the Cham people in the east had gradually been pushed aside or replaced by the resilient Siamese/Thai and Annamese/Vietnamese, respectively. These powers had perceived, understood and increasingly followed the imperative of controlling the lower Mekong basin as the key to control all Indochina. A weak Khmer kingdom only encouraged the strategists in Ayutthaya (later in Bangkok) and in Huế. Attacks on and conquests of Khmer royal residences left sovereigns without a ceremonial and legitimate power base. Interference in succession and marriage policies added to the decay of royal prestige. Oudong was established in 1601 as the last royal residence of the Middle Period.
The 19th century arrival of then technologically more advanced and ambitious European colonial powers with concrete policies of global control put an end to regional feuds and as Siam/Thailand, although humiliated and on the retreat, escaped colonisation as a buffer state, Vietnam was to be the focal point of French colonial ambition.[19] [20] Cambodia, although largely neglected, had entered the Indochinese Union as a perceived entity and was capable to carry and reclaim its identity and integrity into modernity.
After 80 years of colonial hibernation, the brief episode of Japanese occupation during World War II, that coincided with the investiture of king Sihanouk was the opening act for the irreversible process towards re-emancipation and modern Cambodian history. The Kingdom of Cambodia (1953–70), independent since 1953, struggled to remain neutral in a world shaped by polarisation of the nuclear powers USA and Soviet Union. As the Indochinese war escalates, Cambodia becomes increasingly involved, the Khmer Republic is one of the results in 1970, another is civil war. 1975, abandoned and in the hands of the Khmer Rouge, Cambodia endures its darkest hour - Democratic Kampuchea and its long aftermath of Vietnamese occupation, the People's Republic of Kampuchea and the UN Mandate towards Modern Cambodia since 1993.

Funan Kingdom (1st century – 550)
Main article: Kingdom of Funan
Map of Funan at around the 3rd century.
Chinese annals contain detailed records of the first known organised polity, the thalassocratic Kingdom of Funan, on Cambodian and Vietnamese territory characterised by "high population and urban centers, the production of surplus food...socio-political stratification [and] legitimized by Indian religious ideologies". Centered around the lower Mekong and Bassac rivers from the first to sixth century C.E. with "walled and moated cities" such as Angkor Borei in Takeo Province and Óc Eo in modern An Giang Province, Vietnam.

Early Funan was composed of loose communities, each with its own ruler, linked by a common culture and a shared economy of rice farming people in the hinterland and traders in the coastal towns, who were economically interdependent, as surplus rice production found its way to the ports.

By the second century C.E. Funan controlled the strategic coastline of Indochina and the maritime trade routes. Cultural and religious ideas reached Funan via the Indian Ocean trade route. Trade with India had commenced well before 500 BC as Sanskrit hadn't yet replaced Pali. Indian author Dr. Pragya Mishra observes: "Funan Was One Of The Colonies Established By Indians Within Cambodia...[sic]" in his essay "Cultural History of Indian Diaspora in Cambodia". Funans language has been determined as to have been an early form of Khmer and its written form was Sanskrit.

The territories of Eastern Wu (in green), 262 C.E.
Roman trade with India according to the Periplus Maris Erythraei, 1st century CE.
In the period 245-250 C.E. dignitaries of the Chinese Kingdom of Wu visited the Funan city Vyadharapura. Envoys Kang Tai and Zhu Ying defined Funan as to be a distinct Hindu culture. Trade with China had begun after the southward expansion of the Han Dynasty, around the 2nd century B.C. Effectively Funan "controlled strategic land routes in addition to coastal areas" and occupied a prominent position as an "economic and administrative hub" between The Indian ocean trade network and China, collectively known as the Maritime Silk Road. Trade routes, that eventually ended in distant Rome are corroborated by Roman and Persian coins and artefacts, unearthed at archaeological sites of 2nd and 3rd century settlements.

Funan is associated with myths, such as the Kattigara legend and the Khmer founding legend in which an Indian Brahman or prince named Preah Thaong in Khmer, Kaundinya in Sanskrit and Hun-t’ien in Chinese records marries the local ruler, a princess named Nagi Soma (Lieu-Ye in Chinese records), thus establishing the first Cambodian royal dynasty.

Scholars debate as to how deep the narrative is rooted in actual events and on Kaundinya's origin and status. A Chinese document, that underwent 4 alterations and a 3rd-century epigraphic inscription of Champa are the contemporary sources. Some scholars consider the story to be simply an allegory for the diffusion of Indic Hindu and Buddhist beliefs into ancient local cosmology and culture whereas some historians dismiss it chronologically.

Chinese annals report that Funan reached its territorial climax in the early 3rd century under the rule of king Fan Shih-man, extending as far south as Malaysia and as far west as Burma. A system of mercantilism in commercial monopolies was established. Exports ranged from forest products to precious metals and commodities such as gold, elephants, ivory, rhinoceros horn, kingfisher feathers, wild spices like cardamom, lacquer, hides and aromatic wood. Under Fan Shih-man Funan maintained a formidable fleet and was administered by an advanced bureaucracy, based on a "tribute-based economy, that produced a surplus which was used to support foreign traders along its coasts and ostensibly to launch expansionist missions to the west and south".

Historians maintain contradicting ideas about Funan's political status and integrity. Miriam T. Stark calls it simply Funan: [The]"notion of Fu Nan as an early "state"...has been built largely by historians using documentary and historical evidence" and Michael Vickery remarks: "Nevertheless, it is...unlikely that the several ports constituted a unified state, much less an 'empire'". Other sources though, imply imperial status: "Vassal kingdoms spread to southern Vietnam in the east and to the Malay peninsula in the west" and "Here we will look at two empires of this period...Funan and Srivijaya".

The question of how Funan came to an end is in the face of almost universal scholarly conflict impossible to pin down. Chenla is the name of Funan's successor in Chinese annals, first appearing in 616/617 C.E.
...the fall of Funan was not the result of the shifting of maritime trade route from the Malay Peninsula route to the Strait of Malacca starting from the 5th century CE; rather, it suggests that the conquest of Funan by Zhenla was the exact reason for the shifting of maritime trade route in the 7th century CE....

"As Funan was indeed in decline caused by shifts in Southeast Asian maritime trade routes, rulers had to seek new sources of wealth inland."

"By the end of the fifth century, international trade through southeast Asia was almost entirely directed through the Strait of Malacca. Funan, from the point of view of this trade, had outlived its usefulness."

"Nothing in the epigraphical record authorizes such interpretations; and the inscriptions which retrospectively bridge the so- called Funan-Chenla transition do not indicate a political break at all."

The archaeological approach to and interpretation of the entire early historic period is considered to be a decisive supplement for future research. The "Lower Mekong Archaeological Project" focuses on the development of political complexity in this region during the early historic period. LOMAP survey results of 2003 to 2005, for example, have helped to determine that "...the region’s importance continued unabated throughout the pre-Angkorian period...and that at least three [surveyed areas] bear Angkorian-period dates and suggest the continued importance of the delta."

Chenla Kingdom (6th century – 802)
Ancient Khmer script
The History of the Chinese Sui dynasty contains records that a state called Chenla sent an embassy to China in 616 or 617 C.E. It says, that Chenla was a vassal of Funan, but under its ruler Citrasena-Mahendravarman conquered Funan and gained independence.

Most of the Chinese recordings on Chenla, including that of Chenla conquering Funan, have been contested since the 1970s as they are generally based on single remarks in the Chinese annals, as author Claude Jacques emphasised the very vague character of the Chinese terms 'Funan' and 'Chenla', while more domestic epigraphic sources become available. Claude Jacques summarises: "Very basic historical mistakes have been made" because "the history of pre-Angkorean Cambodia was reconstructed much more on the basis of Chinese records than on that of [Cambodian] inscriptions" and as new inscriptions were discovered, researchers "preferred to adjust the newly discovered facts to the initial outline rather than to call the Chinese reports into question".

The notion of Chenla's centre being in modern Laos has also been contested. "All that is required is that it be inland from Funan." The most important political record of pre-Angkor Cambodia, the inscription K53 from Ba Phnom, dated AD 667 does not indicate any political discontinuity, either in royal succession of kings Rudravarman, Bhavavarman I, Mahendravarman [Citrasena], Īśānavarman, and Jayavarman I or in the status of the family of officials who produced the inscription. Another inscription of a few years later, K44, 674 AD, commemorating a foundation in Kampot province under the patronage of Jayavarman I, refers to an earlier foundation in the time of King Raudravarma, presumably Rudravarman of Funan, and again there is no suggestion of political discontinuity.

The History of the T'ang asserts that shortly after 706 the country was split into Land Chenla and Water Chenla. The names signify a northern and a southern half, which may conveniently be referred to as Upper and Lower Chenla.

By the late 8th century Water Chenla had become a vassal of the Sailendra dynasty of Java - the last of its kings was killed and the polity incorporated into the Javanese monarchy around AD 790. Land Chenla acquired independence under Jayavarman II in 802 C.E.

The Khmers, vassals of Funan, reached the Mekong river from the northern Menam River via the Mun River Valley. Chenla, their first independent state developed out of Funanese influence.

Ancient Chinese records mention two kings, Shrutavarman and Shreshthavarman who ruled at the capital Shreshthapura located in modern day southern Laos. The immense influence on the identity of Cambodia to come was wrought by the Khmer Kingdom of Bhavapura, in the modern day Cambodian city of Kampong Thom. Its legacy was its most important sovereign, Ishanavarman who completely conquered the kingdom of Funan during 612-628. He chose his new capital at the Sambor Prei Kuk, naming it Ishanapura.

Khmer Empire (802–1431)
Archers mounted on elephants
Map of South-east Asia c. 900 AD, showing the Khmer Empire in red, Champa in yellow and Haripunjaya in light Green plus additional surrounding states.
The six centuries of the Khmer Empire are characterised by unparalleled technical and artistic progress and achievements, political integrity and administrative stability. The empire represents the cultural and technical apogee of the Cambodian and Southeast Asian pre-industrial civilization.

The Khmer Empire was preceded by Chenla, a polity with shifting centres of power, which was split into Land Chenla and Water Chenla in the early 8th century. By the late 8th century Water Chenla was absorbed by the Malays of the Srivijaya Empire and the Javanese of the Shailandra Empire and eventually incorporated into Java and Srivijaya. Jayavarman II, ruler of Land Chenla, initiates a mythical Hindu consecration ceremony at Mount Kulen (Mount Mahendra) in 802 C.E., intended to proclaim political autonomy and royal legitimacy. As he declared himself devaraja - god king, divinely appointed and uncontested, he simultaneously declares independence from Shailandra and Srivijaya. He established Hariharalaya, the first capital of the Angkorean area near the modern town of Roluos.

Jayavarman II's successors continued to reside north of the Tonlé Sap lake. This population centre was subject to extensive urban planning, embedded in an elaborate hydraulic network of water reservoirs and canals around central monumental religious structures. The religious monuments underwent over the course of several centuries a sophisticated architectural, stylistic and aesthetic development of eventually most exquisite expression and mastery of composition.

Bakong, one of the earliest temple mountain in Khmer architecture
Indravarman I (877 - 889) and his son and successor Yasovarman I (889 - 900), who established the capital Yasodharapura ordered the construction of huge water reservoirs (barays) north of the capital. The water management network depended on elaborate configurations of channels, ponds and embankments built from huge quantities of clayey sand, the available bulk material on the Angkor plain. Dikes of the East Baray still exist today, which are more than 7 km (4 mi) long and 1.8 km (1 mi) wide. The largest component is the West Baray, a reservoir about 8 km (5 mi) long and 2 km (1 mi) across, containing approximately 50 million m3 of water.

Royal administration was based on the religious idea of the Shivaite Hindu state and the central cult of the sovereign as warlord and protector - the "Varman". This centralised system of governance appointed royal functionaries to provinces. The Mahidharapura dynasty - its first king was Jayavarman VI (1080 to 1107), which originated west of the Dângrêk Mountains in the Mun river valley discontinued the old "ritual policy", genealogical traditions and crucially, Hinduism as exclusive state religion. Some historians relate the empires' decline to these religious discontinuities.

Baphuon, a temple-mountain dedicated to the Hindu God Shiva.
The area that comprises the various capitals was spread out over around 1,000 km2 (386 sq mi), it is nowadays commonly called Angkor. The combination of sophisticated wet-rice agriculture, based on an engineered irrigation system and the Tonlé Sap's spectacular abundance in fish and aquatic fauna, as protein source guaranteed a regular food surplus. Recent Geo-surveys have confirmed that Angkor maintained the largest pre-industrial settlement complex worldwide during the 12th and 13th centuries - some three quarters of a million people lived there. Sizeable contingents of the public workforce were to be redirected to monument building and infrastructure maintenance. A growing number of researchers relates the progressive over-exploitation of the delicate local eco-system and its resources alongside large scale deforestation and resulting erosion to the empires' eventual decline.