With the establishment of the People's Republic of China on October 1, 1949, and the arrival of the People's Liberation Army at the Vietnam border in December, a new era began of intense and intimate cooperation between China and Vietnam. Party-to-party relations between the Vietnam Workers Party (VWP) and the Chinese Communist Party formed the core of the relationship, while state-to-state relations between the People's Republic of China and the Democratic Republic of Vietnam, established in January 1950, provided the public form.

Of course, the situations of China and Vietnam over the next twenty-five years were quite different. China had finished its civil war in 1949 and had stabilized by 1952. Its major troubles of the period were largely self-imposed: the Great Leap Forward of 1958–60 and the Cultural Revolution of 1966–69. Only after Mao Zedong's death in 1976 could China begin to change its leftist policies. By contrast, the Democratic Republic of Vietnam in 1950 was still waging a desperate war with French colonial forces. Over the next four years, with Chinese help, it grew into a major and finally a victorious challenge to colonialism, and then became the government of northern Vietnam. In the 1960s the effort to reunify Vietnam began again, and in 1965–73 American direct intervention greatly increased the costs and risks of the war effort.