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.Attacks on and conquests of Khmer royal residences left sovereigns without a ceremonial and legitimate power base.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.
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, 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.
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.
A new dynasty of provincial origin introduced Buddhism, which according to some scholars resulted in royal religious discontinuities and general decline. 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 mid 15th century.