In 1950, the People's Republic of China extended diplomatic recognition to the Viet Minh's Democratic Republic of Vietnam and sent weapons, as well as military advisors led by Luo Guibo to assist the Viet Minh in its war with the French. The first draft of the 1954 Geneva Accords was negotiated by French Prime Minister Pierre Mendès France and Chinese Premier Zhou Enlai who, fearing U.S. intervention, urged the Viet Minh to accept a partition at the 17th parallel.
China's ability to aid the Viet Minh declined when Soviet aid to China was reduced following the end of the Korean War in 1953. Moreover, a divided Vietnam posed less of a threat to China. China provided material and technical support to the Vietnamese communists worth hundreds of millions of dollars. Chinese-supplied rice allowed North Vietnam to pull military-age men from the paddies and imposed a universal draft beginning in 1960.
In the summer of 1962, Mao Zedong agreed to supply Hanoi with 90,000 rifles and guns free of charge. Starting in 1965, China sent anti-aircraft units and engineering battalions to North Vietnam to repair the damage caused by American bombing, rebuild roads and railroads, and to perform other engineering works. This freed North Vietnamese army units for combat in the South.
Sino-Soviet relations soured after the Soviets invaded Czechoslovakia in August 1968. In October, the Chinese demanded North Vietnam cut relations with Moscow, but Hanoi refused. The Chinese began to withdraw in November 1968 in preparation for a clash with the Soviets, which occurred at Zhenbao Island in March 1969. The Chinese also began financing the Khmer Rouge as a counterweight to the Vietnamese communists at this time. China's withdrawal from Vietnam was completed in July 1970.
The Khmer Rouge launched ferocious raids into Vietnam in 1975–1978. Vietnam responded with an invasion that toppled the Khmer Rouge. In response, China launched a brief, punitive invasion of Vietnam in 1979.