The Demographic Transition Model
Every country's population history follows a recognizable shape — birth rate and death rate moving through four (sometimes five) stages. This is one of the AP exam's most heavily tested named models.
Stage 1 describes a pre-industrial society: both birth rate and death rate are high, so they roughly cancel out and total population stays fairly flat. No country in the world remains in Stage 1 today — it’s a historical baseline.
Stage 2 begins when death rate falls sharply — driven by better food supply, sanitation, and basic medicine — while birth rate stays high. That widening gap produces the fastest population growth of any stage. In Stage 3, birth rate finally starts to fall too, driven by urbanization, education, and access to family planning, so growth slows even though the population is still increasing.
By Stage 4, both rates have settled at a similarly low level and population growth levels off. Some versions of the model add a Stage 5, where birth rate actually falls below death rate and the population begins to shrink — a pattern seen today in countries like Japan. One important caveat: the model was built from the historical experience of Western Europe and North America during industrialization, which is why geographers debate whether every country will necessarily follow the same path.