The earliest kingdoms were established in Cambodia in the 1st century AD, but the present-day population looks back to the Khmer Empire that flourished from the 9th century to the 13th century with a great deal of pride. The Khmer Empire, with Angkor Thom as its capital, expanded over time to include present-day Thailand, Cambodia, Laos and southern Vietnam.

With the decline of the Khmer Empire, Cambodia came under repeated attack from neighbouring city-states in Thailand and Vietnam. From the 15th century Cambodia lost people and territory to Thailand in the west, Laos in the north and Vietnam in the east. Battambang was ceded to Thailand in 1809. The continuing conflict meant that by the mid-19th century the population of Cambodia had been reduced to only about 1 million people, less than a quarter of it's previous peak. As a result, in 1854 the King of Cambodia appealed to the French for protection. This was formalised in 1863 when Cambodia became a protectorate of France. From 1887 the country formed part of French indochina.

In 1941 Prince Norodom Sihanouk became King of Cambodia. At the end of 1941 Indochina was invaded by Japan, but the Vichy French administration was allowed to continue the day-to-day running of the country. A border war with Thailand resulted in three western provinces being occupied by Thailand for a time. In March 1945 the fall of the Vichy French government in Europe left a power vacuum in Indochina. The Japanese encouraged King Sihanouk to declare independence although their forces remained in effective control. Following the surrender of Japan in August 1945, France moved to reassert it's control of Indochina, but was forced to agree Cambodia becoming an "autonomous state within the French Union".

Throughout Indochina, but principally in Vietnam, armed left-wing groups began a fierce campaign for independence from France. Within Cambodia radical opposition to the King was also growing. France's failure to regain control of Vietnam eventually prompted Sihanouk to make a decisive move. In January 1953 he dissolved parliament, declared martial law and asserted full independence for Cambodia. In November 1953 France reluctantly accepted the situation. At the Geneva Conference in May 1954, Sihanouk's government was recognised as the sole legitimate authority in the country.

In a further political manoeuvre to outflank the radicals, King Sihanouk abdicated in March 1955 in favour of his father, and created a new mass political movement - People's Socialist Community - which won every seat in parliament that September. Sihanouk ran the country as Prime Minister until his father's death in 1960, whereupon he took the position of Chief of State, rather than monarch. For the next five years Cambodia tried to remain neutral in the fight between communist and non-communist nations, but in 1965 diplomatic relations with the USA were broken-off after South Vietnamese aircraft attacked Viet Cong forces within Cambodia. Henceforth, the Vietnamese communists were officially allowed to use bases in Cambodia. This move seriously eroded right-wing support for the government.

In 1970, while Sihanouk was out of the country, a right-wing coup led by General Lon Nol deposed him and declared a Khmer Republic. The monarchy was abolished and the new government demanded the withdrawal of 40,000 North Vietnamese troops based in the country. Sihanouk formed a government in exile and Beijing and allied himself with former political opponents who controlled the growing Chinese-backed 'Khmer Rouge' left wing guerrilla army.

Meanwhile, the pro-US government in Phnom Penh faced armed opposition from Vietnamese and indigenous Khmer Rouge forces. Heavy military and economic aid from the USA was backed up with military intervention by US and South Vietnamese forces. Despite this support the guerrillas gradually took control of the countryside, and then the provincial capitals and finally, on 17 April 1975, Phnom Penh itself.

The new Khmer Rouge regime under Pol Pot renamed the country Democratic Kampuchea. In an attempt to eradicate pre-revolutionary society, all urban dwellers were forcibly evacuated to the countryside to become agricultural workers. An estimated 1.7 million people - almost a third of the population - are killed during brutal purges over the next four years. Thousands fled the country, seeking refuge in neighbouring countries.

Border clashes with Vietnam in 1978 led to a full-scale invasion of Cambodia later in the year, with Phnom Penh being captured on 7 January 1979. The Khmer Rouge leadership fled to the border regions and was replaced by a new government under Heng Samrin. The country was renamed the People's Democratic Republic of Kampuchea. Stability renamed elusive as the Vietnamese army waged repeated anti-guerrilla campaigns in the western border areas.

In 1982 the principal left-wing and right-wing anti-Vietnamese Khmer forces formed a coalition to combat Vietnam's continued military occupation of their homeland. Peace talks between all the warring factions were first held in 1988. In 1989 Vietnam announced that it would withdraw it's remaining troops by the end of September. That year a new constitution was adopted which renamed the country the State of Cambodia. A ceasefire between the four factions involved in the civil war was agreed in May 1991, and was followed up with an agreement to form a Supreme National Council (SNC) headed by Sihanouk.

United Nations organised polls held in May 1993 saw the election of Sihanouk and his Royalist party to lead the new government. In the following September the monarchy was restored and Sihanouk was again crowned King of Cambodia. Fighting between the Khmer Rouge and government forces continued, but in August 1996 more than half the Khmer Rouge troops accepted a government offer of amnesty. The split in Khmer Rouge ranks resulted in a hard-line faction under Pol Pot retreating into the jungle. By the time of Pol Pot's death in 1998, the Khmer Rouge was rapidly losing support and within a year was largely a spent force.

With the end of several decades of internal fighting, Cambodia could now concentrate on rebuilding it's economy. A series of coalition governments have implemented important economic reforms which in 2002 resulted in international donors pledging $560 million in aid. The country's shattered infrastructure is slowly being rebuilt and the tourist industry is of growing economic importance.

In October 2004 King Sihanouk abdicated in favour of his son Noromdom Sihamoni.