After Vietnamese forces and exiled Cambodians invaded Cambodia in January, 1979, Cambodia got a pro-Vietnamese, moderate communist government and was declared the People’s Republic of Kampuchea. Again, a new flag and national anthem was adopted.
While Vietnam and most Communist governments recognized the new government, the exiled Khmer Rouge, together with the monarchists, formed a government-in-exile that continued to use the former anthem of the Khmer Rouge government; it was this government-in-exile that was recognized by most Western governments and the United Nations. As such, many Western sources continued to list Dap Prampi Mesa Chokchey as the Cambodian national anthem until the return of the monarchy in 1993.
In 1989, the pro-Vietnamese government, in an attempt to gain greater international recognition, changed the state symbols, including the national anthem, in 1989 and renamed the country “State of Cambodia”. Not much is known about the anthem used by the de facto government from 1989-1991. In 1991, a UN peace plan was signed, and the United Nations Transitional Authority in Cambodia (UNTAC) assumed administrative responsibility for Cambodia in March 1992. Some sources mention a textless tune, composed by Prince Ranariddh, was used as the national anthem during the time of the UNTAC administration, yet, like the previous anthem used by the pro-Vietnamese government, not much is known about this anthem. In 1993, the monarchy was restored and universally recognized as the government of Cambodia.
Special thanks to: Jan Scotland for some of this information.