Unintended consequences

China's One-Child Policy leading to doubling of crime rates:

When the Chinese government instituted the policy in 1979, it touched off a wave of sex-selective abortions as pregnant couples decided that if they could have only one child they would benefit most from having a boy. That helped leave modern China with the largest gender imbalance in the world. Today, there are 37 million more men than women in China, and many of the boys are growing up unable to find a job or start a family.