1. China and India have historically been very large sized nations as opposed to European and other countries. So large nations obviously means large population,
2. People used to have large number of children, because few would survive beyond age 5 due to disease and malnutrition. The average longevity in India in 1947 was just 38 years, but now it is over 60.
3. Post-independence, health services were expanded and child mortality came down. This also caused an increase in life span. But the rate of child bearing came down much more slowly, which led to a population explosion.
4. With improving health care and education, and less fear of a child dying, the rate of growth has been coming down. In the southern states, where education and health services are better, it has actually now reached a stable level.
5. The rise of industry and large-scale agriculture meant that families could be much bigger than they had been in the past.
6. The social effects of the rural-urban divide led to more complex societies, more cities, and many more people.
