Third Indochina War

The People's Republic of China had been convenient allies during the Vietnam War despite being traditional enemies. With the American defeat in 1975 it would not take long for the traditional animosity to become the norm once again. Once the communist victory was secured in Vietnam the new communist government began perusing relations with the Soviet Union. However with the Sino-Soviet split and the PRC's improving relations with the United States, Vietnam's ties with Moscow would contribute to increasing tensions between Vietnam and the PRC. Tensions further increased with Vietnam's 1978 invasions of Laos and Cambodia and with Vietnam's expulsion of ethnic Chinese in Vietnam.

On February 17, 1979 about 120,000 Chinese forces invaded Vietnam and seized several Vietnamese towns. Vietnamese forces put up stiff resistance, including using divisions that had been relocated from Cambodia, but the PRC was able to advance about 25 miles into Vietnamese territory and were able to capture the important northern town of Lang Son. A separate Chinese force attacked the coastal town of Quang Yen and captured it after several days of intense fighting. The Vietnamese attempted their own counter-offensive into the PRC's Yunnan province but were pushed back. The PRC withdrew its forces less than one month later, having declared their operations a success. No final treaty or settlement was ever reached.