Claim: Cambodia's deposed king gave support to the Khmer Rouge following the coup in 1970.

Cambodia -LRB- -LSB- kæmˈboʊdiə -RSB- កម ព ជ , or Kampuchea -LSB- kɑmpuˈciə -RSB- -RRB- , officially known as the Kingdom of Cambodia -LRB- ព រ រ ជ ណ ចក រកម ព ជ , Preăh Réachéanachâk Kâmpŭchéa , -LSB- ˈprĕəh riəciənaːˈcɑk kɑmpuˈciə -RSB- -RRB- , is a country located in the southern portion of the Indochina Peninsula in Southeast Asia . It is 181035 km2 in area , bordered by Thailand to the northwest , Laos to the northeast , Vietnam to the east , and the Gulf of Thailand to the southwest .   Cambodia has a population of over 15 million . The official religion is Theravada Buddhism , practiced by approximately 95 percent of the population . The country 's minority groups include Vietnamese , Chinese , Chams , and 30 hill tribes . The capital and largest city is Phnom Penh , the political , economic , and cultural centre of Cambodia . The kingdom is a constitutional monarchy with Norodom Sihamoni , a monarch chosen by the Royal Throne Council , as head of state . The head of government is Hun Sen , who is currently the longest serving non-royal leader in South East Asia and has ruled Cambodia for over 25 years .   In 802 AD , Jayavarman II declared himself king , uniting the warring Khmer princes of Chenla under the name `` Kambuja '' . This marked the beginning of the Khmer Empire which flourished for over 600 years , allowing successive kings to control and exert influence over much of Southeast Asia and accumulate immense power and wealth . The Indianized kingdom built monumental temples including Angkor Wat , now a World Heritage Site , and facilitated the spread of first Hinduism , then Buddhism to much of Southeast Asia . After the fall of Angkor to Ayutthaya in the 15th century , a reduced and weakened Cambodia was then ruled as a vassal state by its neighbours . In 1863 Cambodia became a protectorate of France which doubled the size of the country by reclaiming the north and west from Thailand .   Cambodia gained independence in 1953 . The Vietnam War extended into the country with the US bombing of Cambodia from 1969 until 1973 . Following the Cambodian coup of 1970 , the deposed king gave his support to his former enemies , the Khmer Rouge . The Khmer Rouge emerged as a major power , taking Phnom Penh in 1975 and later carrying out the Cambodian Genocide from 1975 until 1979 , when they were ousted by Vietnam and the Vietnamese-backed People 's Republic of Kampuchea in the Cambodian -- Vietnamese War -LRB- 1979 -- 91 -RRB- . Following the 1991 Paris Peace Accords , Cambodia was governed briefly by a United Nations mission -LRB- 1992 -- 93 -RRB- . The UN withdrew after holding elections in which around 90 percent of the registered voters cast ballots . The 1997 coup placed power solely in the hands of Prime Minister Hun Sen and the Cambodian People 's Party , who remain in power .   The country faces numerous challenges . Important sociopolitical issues includes widespread poverty , pervasive corruption , lack of political freedoms , low human development , and a high rate of hunger . Cambodia has been described by Human Rights Watch 's Southeast Asian Director , David Roberts , as a `` vaguely communist free-market state with a relatively authoritarian coalition ruling over a superficial democracy . '' While per capita income remains low compared to most neighbouring countries , Cambodia has one of the fastest growing economies in Asia with growth averaging 6 percent over the last decade . Agriculture remains the dominant economic sector , with strong growth in textiles , construction , garments , and tourism leading to increased foreign investment and international trade . Cambodia scored dismally in an annual index -LRB- 2015 -RRB- ranking the rule of law in 102 countries , placing 99th overall and the worst in the region .   Cambodia also faces environmental destruction as an imminent problem . The most severe activity in this regard is considered to be the countrywide deforestation , which also involves national parks and wildlife sanctuaries . Overall , environmental destruction in Cambodia comprise many different activities , including illegal logging , poaching of endangered and endemic species , and destruction of important wildlife habitats from large scale construction projects and agricultural businesses . The degrading activities involve the local population , Cambodian businesses and political authorities , as well as foreign criminal syndicates and many transnational corporations from all over the world .