The Demographic Transition Model
A model used to represent the process of explaining the transformation from a pre-industrial to an industrialized economy. It has 4 definitive stages:
In stage one (high stationary), pre-industrial society, death rates and birth rates are high and roughly in balance.
In stage two (early expanding), that of a developing country, the death rates drop rapidly due to improvements in food supply and sanitation, but without a corresponding fall in birth rates this produces an imbalance, resulting in a large increase in population.
In stage three (late expanding), birth rates fall due to access to contraception, increases in wages, urbanization, a reduction in subsistence agriculture, an increase in the status and education of women, a reduction in the value of children's work, an increase in parental investment in the education of children and other social changes. Population growth slows.
In stage four (low stationary) there are both low birth rates and low death rates due to the expansion of wealth and technology.
"Stage five" (hypothetical), birth rates may drop to well below replacement level as has happened in countries like Germany, Italy, and Japan, leading to a shrinking population. This may be a threat to many industries that rely on population growth, and would likely create an economic burden on the shrinking working population.