the Vietnamese launched another limited counter-attack in June, forcing the Kampucheans to retreat. Again the Vietnamese withdrew and the Kampucheans resumed their attacks. The Vietnamese had had enough; in December 1978, Vietnam launched a full-scale invasion. Phnom Penh was captured in January 1979, the ruling Khmer Rouge were driven from power and a pro-Vietnamese government was installed. In 1984, Vietnam unveiled a plan for the disengagement of its army from Kampuchea. In 1988, the Vietnamese Government began withdrawing forces in earnest; the last men left in September 1989. The Third Indochina War also refers to the Sino-Vietnamese War, which was fought in February–March 1979 between the People's Republic of China and the Socialist Republic of Vietnam. Shortly after the Vietnamese invasion of Cambodia, the People's Republic of China, who were the Khmer Rouge's political ally, launched a punitive invasion of Vietnam. Fighting was short but intense. The Chinese advanced about forty kilometers into Vietnam, occupying the city of Lang Son on 6 March. There, they claimed the gate to Hanoi was open, declared their punitive mission achieved, and withdrew. On 23 October 1991, the Cambodian-Vietnamese War was officially declared over as a result of negotiations and the signing of 1991 Paris Peace Agreements. See also Korean War Sino-Soviet split References Further reading 20th century in Cambodia 20th century in Laos 20th century in Vietnam Cold War conflicts Wars involving Cambodia Wars involving Laos Wars involving Vietnam