Heng Samrin
In December 1978, Vietnam announced the formation of the Kampuchean United Front for National Salvation (KUFNS) under Heng Samrin, a former DK division commander. It was composed of Khmer Communists who had remained in Vietnam after 1975 and officials from the eastern sector—like Heng Samrin and Hun Sen—who had fled to Vietnam from Cambodia in 1978. In late December 1978, Vietnamese forces launched a full invasion of Cambodia, capturing Phnom Penh on 7 January 1979 and driving the remnants of Democratic Kampuchea's army westward toward Thailand.