Richardson' study of China's influence on the establishment of the rebel government (
GRUNK), Sihanouk's relationship with the Khmer Rouge, and China's response to the Khmer Rouge victory in 1975 are important contributions to scholarship.
Later he became Cambodia's Ambassador in Egypt, and in 1970 he became Foreign Minister for the Royal Government for the National Unification of Kampuchea (
GRUNK), the pro-Sihanouk government in-exile established by a broad coalition of leftists and neutralists, based in Beijing, China.