Demographic Transition
Some researchers have made the claim that we may never reach Earth's carrying capacity because of the patterns that have been observed throughout the world. The UN predicts that we will reach roughly 11 billion people in the year 2100 and that will be the peak population size before it begins to drop. Demographic transition explains the economic and social changes that occur as countries develop and industrialize.
Stage One: Pre-industrial
Birth rates and death rates are both high in a pre-industrialized society. Death rates are high due to a lack of healthcare and unstable food supplies. Birth rates are high due to high IMR, lack of contraceptive use, and the need for children to help with labor, as economies are mainly agriculture-based here. Due to the high birth and death rates, populations typically do not grow much at this stage.
Stage Two: Industrialization
This second stage is the "transition stage" where the population is transitiong from a pre-industrial society to an industrial society. Increased food production, better sanitation, and better healthcare results in rapidly falling death rates. TFR remains high, however, due to most people not having adjusted to the new social structures, This results in rapid population growth.
Stage Three: Industrialized
Industrialized societies experience significantly higher affluence. Increased employment and educational opportunties, especially for women, result in a lower TFR due to later age of marriage and later age of having the first child. As children are no longer needed for labor, there is less pressure to have large families. This, coupled with increased contraceptive use, results in a drop in birth rates, with reduced population growth.
Stage Four: Post Industrialized
As societies continue to develop and modernize, the birth and death rates continued to drop and reached stable points and fairly low levels. This results in stable populations, including some where the population actually begins to shrink.