But the interesting part is here:
Another source of Vietnamese anger at China is the growing Chinese recruiting of Vietnamese women to be prostitutes or brides in China. This problem began in the late 1970s when, to control population growth most Chinese couples were restricted to only one child. This has been widely enforced, to the point where the average number of children per couple has been 1.7. But many of those couples aborted a child if it was a female, because much more importance is attached to having a male heir. Thus there are 35 million more males than females in China, and the disparity is growing. These surplus males are coming of age, and the competition for wives is causing problems. Women are taking advantage of their scarcity, but men are also going to neighboring countries to buy, or even kidnap, young women to be wives. This is causing ill will with neighbors, especially Vietnam.