After being seized by the Thai army in 1431, it appeared that the Angkor entered a Dark period as there were rarely any inscription found in later centuries. There are two theories being disputed by the historians about the destiny of Angkor after this year. The first theory said that the city of Angkor was completely abandoned due to the Thai's onslaught and the people fled to take up residence in the south somewhere around 40 km north of Phnompenh. Another theory suggested that the city of Angkor was not completely abandoned at that time, but a different lineage of the Khmer king took the opportunity to establish his own power as a rival state in the south around Phnompenh; the final downfall of the Angkor was actually due to the shift of the economic importance to Phnompenh region which became a growing and flourishing trading center, especially with the Chinese during the 17th and 18th century.
No matter which theory is true; there are undeniable facts to support that the Angkor was not completely forgotten by the people of Khmer. Around 1550-1570, an unknown king of the Angkor attempted to restore a temple without success. Moreover, in the 17th century there were Japanese settlements residing with the Khmer people in the Angkor city, as at least fourteen Japanese inscriptions had been found in the area. One of the most renowned Japanese inscriptions belonged to Ukondafu Kazufusa who had visited the Angkor and celebrated Khmer's New Year there in the year 1632. Anyhow, the city of Angkor was finally abandoned sometimes later, but the definite year and the exact reasons are not known.
Obviously, the West did not know anything about the existence of the Khmer Civilization until a French botanist Henri Mouhot published his finding of this lost empire in 1861 (one year after he rediscovered the Angkor). He was stunned by the magnificence of Angkor Wat and Angkor Thom which were hidden in the jungle. His announcement aroused the interest of the Westerners and subsequently attracted many explorers, historians and archaeologists to further explore and study the lost Khmer Civilization.
Henri Mouhot was often regarded as the "first discoverer" of the lost Angkor Civilization in many text books. It is interesting to point out that Henri Mouhot was not the first European to step upon the land of Angkor. As far back as 1550, a Portugese trader Diogo do Couto visited this land and wrote some accounts about it. Mouhot's contemporary Father Bouilleveaux, who was a French missionary in Battambang, claimed that many other Western missionaries including himself had visited Angkor Wat and the other Khmer temples at least five years before Henri Mouhot.
In 1863, Cambodia became a French colony. After annexing Siemreap (Angkor) and Battambang from Thailand in 1907, the French had established the Angkor Conservation Center in 1908 to conduct archaeological study of the Angkor Civilization as well as to restore the various Khmer temples. These activities were abruptly ended in 1972 due to the outbreak of civil war followed by the reign of terror by Khmer Rouge (1975-1979). Due to the political problem, Cambodia was close from the outer world until 1990, the year of which, the United Nations sponsored the general election.
Angkor Wat and the other Khmer temples are regarded as the World Heritage by UNESCO in 1992. Their survival needs International assistance and funds. Lying in the tropical rain forest, the temples are consistently invaded by overgrown trees whose roots penetrate the temples' foundation whereas the water helps in its decay. The weakening of their foundations endangered the temples to collapse in the future if no preservation works were done. In addition to the natural conditions, the heritage is also endangered from thefts. According to the UN estimates, each piece of the Khmer artifacts could be sold in the black market to as high as USD 30,000 - USD 300,000, and unfortunately, they are kept in the private museums or homes of the few rich men. Such amount of money raised greed, and of course, attracted more than an ordinary theft, but the organized ones. Since 1994, serious actions have been taken by the Cambodian government in the support of UNESCO to prevent those thefts.
The archaeological activities have been restarted by substantial funding from UNESCO in order to preserve this World Heritage for the future generations.
At the time of this writing in the beginning of New Millennium 2000, Angkor Wat and the other Khmer temples still stand magnificently on the vast plain of Siemreap in Cambodia and are one of the main touristic spots in Southeast Asia!