The Cambodian Campaign (also known as the Cambodian Incursion) was a series of military operations conducted in eastern Cambodia during mid-1970 by the United States (U.S.) and the Republic of Vietnam (South Vietnam) during the Vietnam War. These invasions were a result of policy of President Richard Nixon whose decision it was to invade. A total of 13 major operations were conducted by the Army of the Republic of Vietnam (ARVN) between 29 April and 22 July and by U.S. forces between 1 May and 30 June.

The objective of the campaign was the defeat of the approximately 40,000 troops of the People's Army of Vietnam (PAVN) and the National Front for the Liberation of South Vietnam (NLF, also known as Viet Cong) who were ensconced in the eastern border regions of Cambodia. As great a prize as the defeat of these forces was the possibility of the occupation and destruction of large communist base areas and sanctuaries, which had been protected by Cambodian neutrality since their establishment in 1966. As far as the U.S. was concerned, such a course of action would provide a shield behind which the policy of Vietnamization and the withdrawal of U.S. forces from South Vietnam could proceed unmolested.

Cambodia (ⁱ/kæmˈboʊdiə/;Khmer: ព្រះរាជាណាចក្រកម្ពុជា, Kampuchea, IPA: [kɑmˈpuˈciə]), officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia. With a total landmass of 181,035 square kilometres (69,898 sq mi), it is bordered by Thailand to the northwest, Laos to the northeast, Vietnam to the east, and the Gulf of Thailand to the southwest.

With a population of over 14.8 million, Cambodia is the 68th most populous country in the world. The official religion is Theravada Buddhism, which is practiced by around 95% of the Cambodian population. The country minority groups include Vietnamese, Chinese, Chams and 30 various hill tribes. The capital and largest city is Phnom Penh; the political, economic, and cultural center 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 leader in South East Asia and has ruled Cambodia for over 25 years.

Norodom Sihanouk (Khmer: នរោត្តម សីហនុ) (born 31 October 1922) was the King of Cambodia from 1941 to 1955 and again from 1993 until his semi-retirement and voluntary abdication on 7 October 2004 in favour of his son, the current King Norodom Sihamoni. Since his abdication, he has been known as The King-Father of Cambodia (Preahmâhaviraksat), a position in which he retains many of his former responsibilities as constitutional monarch.

The son of King Norodom Suramarit and Queen Sisowath Kossamak, Sihanouk has held so many positions since 1941 that the Guinness Book of World Records identifies him as the politician who has served the world's greatest variety of political offices. These included two terms as King, two as Sovereign Prince, one as president, two as prime minister, and one as Cambodia's non-titled head of state, as well as numerous positions as leader of various governments-in-exile.

Most of these positions were only honorific, including the last position as constitutional King of Cambodia. Sihanouk's actual period of effective rule over Cambodia was from 9 November 1953, when France granted independence to Cambodia, until 18 March 1970, when Lon Nol and the National Assembly deposed Sihanouk.