Political map of China, Japan, Korea, and Mongolia 05 March 1979 (Sino-Vietnamese War): Mao Zedong's death in 1976 led to a two-year power struggle for leadership of China. Meanwhile, Soviet (Soviet Union)-allied North Vietnam annexed South Vietnam and, in late 1978, invaded Chinese-backed Cambodia (Cambodian-Vietnamese War). China responded in early 1979 with an attack on Vietnam (Sino-Vietnamese War). After a month of brutal but inconclusive warfare, the Chinese withdrew.