The conflict between Kampuchea, or Cambodia, and Vietnam dates back to the late 1970s, though tensions between the two regions date back centuries to earlier wars and incursions on both sides. The present conflict came about in 1978 when Hanoi launched an offensive with twelve to fourteen divisions and three Khmer regiments, a total invasion force of 100,000 people. The Vietnamese units crossed the Cambodian frontier in five spearheads, initially directed into northeastern Cambodia. It is believed that in concentrating its forces in this way, Vietnam may have had several objectives. One may have been to capture as quickly as possible substantial expanses of Cambodian territory which had earlier been a spawning ground for the Khmer Rouge in the late 1960s. An early occupation would also have preempted Khmer Rouge units from withdrawing to an areas where they might have a measure of public support. Attacks on the northeast may also have been intended to confuse the leadership in Kampuchea about where the full offensive would fall. However, the Khmer Rouge was not fooled and erected its main defense line in an arc across the flat, rice-growing plains of southeastern Cambodia, and indeed Vietnam forces did launch a full attack in this direction. Heavy fighting was localized. Vietnamese forces pushed through to the capital at Phnom Penh in January 1979 and continued into western Cambodia. The Khmer Rouge forces regrouped in a different way and rekindled an insurgency against the new government, just as they had done in the late 1960s. Insecurity ruled in the countryside in spite of the continued Vietnamese presence.
This was the beginning of a protracted guerrilla war waged by the Khmer Rouge against the occupying forces of Vietnam. The insurgents fomented continuous rebellion in the early 1980s, operating from refugee camps on the Thai frontier to make forays into the Cambodian border provinces and to keep the countryside...