demographic transition model
stage one: the most undeveloped countrys, (e.g. )
there is high birth and death rates, so in balance.
stage two: death rates drop rapidly cause the country is developing.
with a slight fall in birth rate as well, but overall, the population grows.
stage three: due to access to contraception, birth rates go down, and both death and birth rates level off.
stage four: both low birth rates and low death rates.
stage five(?): some theorists consider that a fifth stage is needed to represent countries that have sub-replacement fertility (that is, below 2.1 children per woman).