The history of the regime of Democratic Kampuchea (DK) which ruled Cambodia from 1975 to 1979 in the name of social revolution made on behalf of Cambodia's poor peasants has been researched and documented according to many sources. When the leaders of the counter-revolutionary Kampuchean United Front for National Salvation, spearheaded by a massive force of the People's Army of Vietnam, took back the capital, Phnom Penh, on 7 January 1979, they captured official documents, particularly the forced confessions of thousands of political prisoners, which threw light on the nature of the regime and its catastrophic course after victory in April 1975. Other contemporary sources included monitored radio broadcasts of the regime, the dossiers of Khmer Rouge defectors to Thailand compiled by the US State Department, and the rich vein of information provided to western scholars of Cambodian history by refugees in the Thai camps and in other countries which received them after 1979.