After the 1978 Vietnamese invasion of Cambodia and subsequent collapse of Democratic Kampuchea in 1979, the Khmer Rouge fled to the border regions of Thailand, and, with assistance from China, Pol Pot's troops managed to regroup and reorganize in forested and mountainous zones on the Thai-Cambodian border. During the 1980s and early 1990s Khmer Rouge forces operated from inside refugee camps in Thailand, in an attempt to de-stabilize the pro-Hanoi People's Republic of Kampuchea's government, which Thailand refused to recognise. Thailand and Vietnam faced off across the Thai-Cambodian border with frequent Vietnamese incursions and shellings into Thai territory throughout the 1980s in pursuit of Cambodian guerrillas who kept attacking Vietnamese occupation forces.