1979 why did the sino-Vietnamese border war happen?

The evacuation of overseas Chinese in Cambodia caused great dissatisfaction in Vietnam. It expelled overseas Chinese from China and harassed China in the border areas of the two countries in retaliation.

1, 1975 Vietnam and the United States signed the Paris Agreement, and the Vietnam War ended.

2. After Cambodia's * * * production party came to power with the support of China * * *, it carried out crazy cleansing in Cambodia, and Cambodia * * * killed dissidents with a population of13 at that time.

3. After the Vietnam War, the Vietnamese authorities turned to the Soviet Union and were indifferent to China, which made China very dissatisfied.