Population & Migration: Demographic Transition, Refugees, and Growth

The Demographic Transition Model (DTM)

The DTM is the single most-tested concept in population geography. Countries pass through five stages as they develop:

1. Stage 1: High birth rate, high death rate → stable, low total population. Pre-industrial societies.
2. Stage 2: Death rate drops (medicine, sanitation) but birth rate stays high → rapid population growth. Many developing countries in the mid-20th century.
3. Stage 3: Birth rate begins to fall (urbanization, women's education, contraception) → growth slows. India today.
4. Stage 4: Low birth rate, low death rate → near-zero natural growth. Most high-income countries.
5. Stage 5: Very low birth rate below replacement (2.1 children/woman) → population shrinks and ages. Japan, South Korea, Germany, Italy.

Population pyramids tell you the stage

A population pyramid displays population by 5-year age band and sex. Its SHAPE tells you a country's demographic stage:

• Wide base, narrow top — Stage 2 (high fertility, still-elevated older-age mortality). Niger, Angola.
• Narrower base, thick middle — Stage 3-4 transitioning. Brazil, Mexico.
• Column shape — Stage 4 (stable). US, France.
• Inverted (narrow base, wide top) — Stage 5 (aging, shrinking). Japan, Germany.

Dependency ratio

Dependency ratio = (population under 15 + population 65+) / working-age population (15-64). High ratios pressure the working-age population. Countries in Stage 5 face rising OLD-age dependency; countries in Stage 2 face YOUNG-age dependency. Both create policy challenges but different ones.

Demographic dividend

Between the fertility drop of Stage 3 and the aging of Stage 4/5, a country has an unusually large working-age share and small dependency burden. If invested in productive employment and education, this can boost economic growth. East Asian tigers (South Korea, Taiwan, later China) captured this dividend. Many Sub-Saharan African countries are just entering this window.

Migration typology

Migration classifications:

• International vs internal — crossing borders vs staying within one country
• Voluntary vs forced — economic migrant vs refugee/IDP
• Chain migration — earlier migrants help later migrants from the same origin come and settle in the same destination, producing ethnic-community concentrations
• Step migration — village → town → city → capital → international
• Return migration — moving back to origin (often after retirement)

Refugees vs Internally Displaced Persons

The distinction matters legally and geographically:

• Refugees — have crossed an international border because of a well-founded fear of persecution, war, or violence. Protected under the 1951 Refugee Convention.
• Internally Displaced Persons (IDPs) — similarly forced to flee their homes but remain within their country of origin. Not covered by the Refugee Convention. Often even more vulnerable.

Push-pull factors (Everett Lee 1966)

Migration flows respond to unfavorable origin conditions (push) plus favorable destination opportunities (pull), moderated by intervening obstacles (distance, borders, cost). Both sides matter. Case examples the exam tests:

• Mexico → US — economic (jobs, wages) + family reunification pull; economic push in Mexico earlier decades
• South Asia → Gulf States — construction/service jobs
• Ukraine → EU (2022+) — war-driven refugee flow, one of the fastest large-scale movements in recent European history
• Venezuela → regional South America — economic and political collapse
• Bangladesh → India — labor and periodic climate-driven displacement

Urbanization

Rural-to-urban migration + higher urban natural increase = rapid urbanization. Most of the 21st century's population growth is happening in cities in the developing world. Sub-Saharan African cities — Lagos, Kinshasa, Dar es Salaam, Nairobi, Addis Ababa — are among the world's fastest-growing megacities. Informal settlements (favelas, townships, kampungs) expand where formal housing supply can't keep up.