Update: just out of interest, here is a section from a 2006 paper talking about the possible effects of gender imbalances of the type in China and India:
There is also evidence that, when single young men congregate, the potential for more organized aggression is likely to increase substantially (45, 53). Hudson and Den Boer, in their provocative writings on this subject (45, 46), go further, predicting that these men are likely to be attracted to military or military-type organizations, with the potential to be a trigger for large-scale domestic and international violence. With 40% of the world's population living in China and India, the authors argue that the sex imbalance could impact regional and global security, especially because the surrounding countries of Pakistan, Taiwan, Nepal, and Bangladesh also have high sex ratios.A number of other consequences of an excess of men have been described, but there is very little evidence for causation. It is intuitive that if sexual needs are to be met this will lead to a large expansion of the sex industry, including its more unacceptable practices such as coercion and trafficking. The sex industry has expanded in both India and China in the last decade (55, 56); however, there are a number of reasons for this expansion, and the part played by a high sex ratio is impossible to isolate without specific research addressing this question. Indeed, in China the highest numbers of sex workers are in areas where the sex ratio is least distorted, for example in the border areas of Yunnan Province (57). The recent rise in numbers of sex workers in China has been attributed more to greater mobility, increased socioeconomic inequality, and a relaxation in sexual attitudes, than to an increase in the sex ratio (57, 58).There is much anecdotal evidence regarding increases in trafficking of women, both for the sex industry and marriage, in both India and China (59, 60), although it is impossible to say whether gender imbalance is a contributory factor in this rise. Reports would suggest that trafficking is more common in parts of Africa and Eastern Europe where the sex ratio is normal (61). It has also been suggested that a shortage of women may lead to a rise in homosexual behavior (31), not implying that the shortage of women will produce homosexuals, but rather that an increasing tolerance toward homosexuality, together with the surplus of males, may lead to large numbers of covert homosexuals openly expressing their sexuality.