This national holiday is always celebrated annually on 7 January. Also known as Cambodian Victory Day, it marks the end of the Khmer Rouge regime in 1979.
During the Vietnam war, Cambodia was a base for communist forces, and at the end of that conflict, an offshoot from the Vietnam People's Army called the Khmer Rouge (Red Khmer) took power in 1979.
Mixing the ideology of communism and the Ankor Empire, they implemented extreme communist policies, enforcing strict self-sufficiency and taking children from parents, so they could be indoctrinated in communism.
An aim of the Khmer Rouge was to return Cambodia to a purely agricultural society. To implement this, many Cambodians were forced to leave the cities to work on labour camps.
It is estimated that around two million Cambodians (almost a quarter of the population) were killed in the four years of the Khmer Rouge regime from starvation, illness, overwork in the labour campos or execution for not embracing the ideals of the Khmer Rouge. This led to the reign of the Khmer Rouge under Pol Pot being seen as effectively a campaign of genocide against the Cambodian people.
On 7 January 1979, Vietnamese troops entered Cambodia and began the assault to remove the Khmer Rouge. The Khmer Rouge surrendered on 17 April 1979.
Commemorating such a dark period in history means this holiday is a solemn affair, with the day marked by remembrance services for those who lost their lives.
It is also not a universally welcome holiday in Cambodia as many Cambodians feel uneasy about their dependence for liberation on Vietnam.