Angkor
In the early days of Angkor, the worship of Vishnu was secondary to that of Shiva. The relationship seems to have changed with the construction of Angkor Wat by King Suryavarman II as his personal mausoleum at the beginning of the 12th century. The central religious image of Angkor Wat was an image of Vishnu, and an inscription identifies Suryavarman as "Paramavishnuloka," or "he who enters the heavenly world of Vishnu." Religious syncretism, however, remained thoroughgoing in Khmer society: the state religion of Shaivism was not necessarily abrogated by Suryavarman's turn to Vishnu, and the temple may well have housed a royal lingam. Furthermore, the turn to Vaishnavism did not abrogate the royal personality cult of Angkor. by which the reigning king was identified with the deity. According to Angkor scholar Georges Coedès, "Angkor Wat is, if you like, a vaishnavite sanctuary, but the Vishnu venerated there was not the ancient Hindu deity nor even one of the deity's traditional incarnations, but the king Suryavarman II posthumously identified with Vishnu, consubstantial with him, residing in a mausoleum decorated with the graceful figures of apsaras just like Vishnu in his celestial palace." Suryavarman proclaimed his identity with Vishnu, just as his predecessors had claimed consubstantiation with Shiva.
Early history of Cambodia
Suryavarman II (1113 - 1150), one of the greatest Angkorian monarchs, expanded his kingdom's territory in a series of successful wars against the kingdom of Champa in central Vietnam and the small Mon polities as far west as the Irrawaddy River of Burma. He reduced to vassalage the Thai peoples who had migrated into Southeast Asia from the Yunnan region of southern China and established his suzerainty over the northern part of the Malay Peninsula. His greatest achievement was the construction of the temple city complex of Angkor Wat. The largest religious edifice in the world, Angkor Wat is considered the greatest single architectural work in Southeast Asia. However, territorial expansion came to a halt when Suryavarman II was killed in battle attempting to invade Đại Việt. With Đại Việt's support, the Cham quickly drove Khmer presence out of Champa territory. Suryavarman II's reign was, unfortunately, then followed by thirty years of dynastic upheaval and an invasion in revenge by the neighbouring Cham, who destroyed the city of Angkor in 1177.