The demographic transition model.

The demographic transition model is based on historical population trends of birth rates and death rates. The model explains typically how populations move from high birth and death rates to low birth and death rates through stages:

• Stage 1: High birth and death rates; population growth is slow.
• Stage 2: Death rates decline due to improvements in healthcare and sanitation; birth rates remain high, leading to rapid population growth.
• Stage 3: Birth rates begin to decline due to changes in societal values, increased access to contraception, and women's education.
• Stage 4: Both birth and death rates are low, stabilizing the population growth.
• Stage 5: In some models, birth rates fall below death rates, leading to population decline.

The world has been going through the stages 2, 3, 4 and/or 5 of The demographic transition over the past 100 years.