China's problem: Leftover men

Years of the one-child policy and sex determination caused by preference for boys means there are now 20 million more men under 30 than women. By 2040, there will be 44 million such leftover men of marriageable age.

The challenges leftover men pose to China are staggering, linked as they are to a host of rising problems from prostitution, trafficking and sexually transmitted diseases to violence and even ethnic strife, over an increasingly rare resource - women.

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