China's one-child policy, in effect from 1980 to 2015, was the most dramatic population control experiment in history. The government limited most urban families to a single child, enforced through fines, job loss, and in some cases forced abortions. The goal was to curb population growth and raise per-capita income.

The policy worked — perhaps too well. China's fertility rate fell from 2.6 in 1980 to 1.5 by 2000, well below replacement. But fertility was already falling before the policy, driven by urbanization and education. Some demographers estimate the policy prevented 300–400 million births; others argue the number would have fallen anyway, making the true impact far smaller.

The unintended consequences were severe. A cultural preference for sons, combined with a one-child limit, led to sex-selective abortion. China now has about 30 million more men than women — "surplus males" who will never find partners. The aging population is accelerating: by 2050, China will have more people over 65 than the entire population of the United States.

The policy was relaxed to two children in 2016 and three in 2021, but the birth rate has not recovered. The 2023 fertility rate was around 1.0 — among the lowest in the world. Chinese couples, having internalized the norm of small families, are not responding to government incentives. The lesson: it is far easier to push fertility down than to push it back up.

The one-child policy remains controversial. Supporters argue it helped China escape poverty by reducing the dependency ratio. Critics point to the human rights abuses, the gender imbalance, and the demographic crisis now unfolding. Either way, it is a case study in how government policy can reshape population — and how the effects, intended and unintended, can last for generations.