By the 1970s and 1980s population growth in the industrialized countries had begun to fall significantly. By the 1990s some European leaders were expressing concern that low birthrates threatened national economies by reducing the labor force, the tax base, and the number of consumers. Between 1970 and 1975 China registered the fastest five-year birthrate decline in recorded history. Other countries, especially in Latin America and East Asia, experienced declines in fertility. Fertility in most of the developing world could fall below the replacement level (2.1 children per woman) before 2100.

There were several reasons for this decline in fertility among women in the developing world. As fewer babies died of disease or malnutrition, families needed fewer births to guarantee the survival of the number of children they wanted. Better living conditions, urbanization, and more education encouraged women to have fewer children.

In the early 1960s the introduction of the birth control pill allowed women to take control of their own fertility. Family planning was now truly possible. In the early twenty-first century, more than half of the world’s couples practiced some form of birth control, up from one in eight just forty years earlier.