Unit 2.5 — Migration Causes and Types

Everything so far in Unit 2 has looked at how a population grows or shrinks in place — through births and deaths, tracked by the Demographic Transition Model, and shaped by the resource pressures that Malthus, Boserup, and their successors argued about. But population change has a second engine entirely: people simply relocating. Migration reshuffles population geography on a timescale far faster than birth and death rates ever could, and it is the subject of this lesson and the one that follows it.

Defining migration and its basic vocabulary

Geographers reserve the term migration for a permanent or semi-permanent change of residence, distinguishing it from short-term mobility like a daily commute, a vacation, or seasonal movement (nomadic herding, migrant agricultural labor that returns home after a harvest season). Two directional terms anchor the discussion: emigration is departure from a place (an emigrant leaves), and immigration is arrival into a place (an immigrant enters) — the same move is emigration from the origin's point of view and immigration from the destination's. Net migration is the balance of the two: immigrants minus emigrants for a given place over a given period, and it is the migration counterpart to the rate of natural increase you calculated earlier in this unit — together, net migration and RNI are the only two components of total population change a place can experience.

Migration also splits along a fundamental distance-and-border axis. Internal migration is movement within the borders of a single country — a Texan moving from Lubbock to Dallas, or the much larger historical pattern of rural-to-urban movement inside a country. International migration crosses a political border and is generally the more consequential kind for policy, since it involves a different country's citizenship, labor law, and border-control apparatus on the receiving end.

Push and pull factors

The classic framework for explaining why any specific migration happens is the push-pull model: push factors are conditions that drive people to leave an origin, and pull factors are conditions that draw them toward a destination. Neither operates alone — a real migration decision is nearly always a combination of a push at home and a pull somewhere else, weighed against the real and perceived cost of moving. Geographers typically group these forces into four categories, and being able to sort a given scenario correctly into the right category (rather than just labeling it vaguely "economic") is a core exam skill:

• Economic — the single most common driver of voluntary migration worldwide: unemployment or low wages pushing people out, and job availability or higher wages pulling them in. Labor migration from Mexico and Central America to the United States, and from South and Southeast Asia to the Gulf states, are both overwhelmingly economic in character.
• Political — war, persecution, authoritarian repression, or the collapse of state authority pushing people out, and political stability or asylum protections pulling them toward safer states. Syria's civil war, which began in 2011, produced one of the largest forced-displacement events of the 21st century, pushing more than 6 million Syrians into neighboring countries and Europe.
• Environmental — natural disasters, drought, desertification, or sea-level rise pushing people from land that can no longer support them. The Dust Bowl of the 1930s, which pushed roughly 2.5 million people out of the U.S. Southern Plains (including a large wave from Oklahoma toward California), remains the textbook historical example, and rising concern about climate-driven displacement in low-lying coastal nations like Bangladesh and small Pacific island states is the modern extension of the same category.
• Cultural / social — religious persecution, ethnic conflict, or simply the pull of family and community networks already established at a destination pulling new migrants toward the same place (a mechanism called chain migration, discussed further below).

Ravenstein's laws of migration

English geographer Ernst Georg Ravenstein published a set of generalizations about migration patterns in the 1880s, based on observed 19th-century British census data, and a version of his core observations remains the foundational theoretical model for this topic on the exam. Several of the most testable ideas from Ravenstein's laws:

• Most migrants move only a short distance, and the number of migrants moving between two places decreases as the distance between them increases — a pattern later formalized by other geographers as distance decay.
• Migration happens in steps rather than as one long leap: a rural resident might first move to a nearby market town, then later to a regional city, then possibly on to a national capital — a pattern known as step migration.
• Long-distance migrants tend to move toward major economic and urban centers rather than toward the nearest available destination, because the pull of a large labor market outweighs the extra distance.
• Every migration flow produces a counterflow — some migrants always return or move back the direction they came from, even while the larger flow continues outward.
• Urban residents are less migratory than rural residents, since city dwellers already have access to the economic opportunity that would otherwise be a migration's whole motive.
• Most migrants are young adults, rather than children or the elderly, since young working-age adults face the lowest relative cost (fewest dependents, most remaining working years to recoup the move's cost) and the highest expected economic payoff from relocating.

Ravenstein's laws describe general tendencies observed in a specific 19th-century industrializing context, not universal physical laws — the exam expects you to apply them as a useful predictive framework and to recognize real cases that fit or depart from them, not to treat them as infallible.

Forced versus voluntary migration

A separate and equally important axis sorts migration by how much genuine choice the migrant had. Voluntary migration is a decision made by weighing push and pull factors, even under real hardship — most economic and much environmental migration falls here. Forced migration involves no meaningful choice to stay: refugees fleeing war or persecution, people displaced by a government-ordered relocation, or historically, the transatlantic slave trade, which forcibly transported an estimated 12.5 million enslaved Africans across the Atlantic between the 16th and 19th centuries — the largest forced migration in recorded history and a case with essentially zero voluntary element. The exam distinguishes a refugee (someone who has crossed an international border fleeing persecution or violence, a status defined under the 1951 UN Refugee Convention) from an internally displaced person ("IDP") (someone forced from their home by the same kinds of threats but who has not crossed an international border, and so remains under their own country's jurisdiction rather than international refugee protections) — Syria's displacement crisis, for instance, produced both large refugee flows into neighboring Turkey, Lebanon, and Jordan and an even larger internally displaced population that never left the country.

Chain migration and migration corridors

Chain migration describes how an early migrant from a particular origin community, once established at a destination, becomes a magnet and support network that draws relatives, friends, and other people from the same origin community to the same destination over time — explaining why specific immigrant communities cluster so heavily in specific cities (for instance, the concentration of early-20th-century Sicilian immigrants in specific New York City neighborhoods, or more recent Vietnamese-American concentration in parts of Houston and Orange County, California). This mechanism reinforces Ravenstein's observation about counterflows and clustering: migration streams are rarely evenly distributed across a destination country; they follow the specific corridors earlier migrants already built.

Why this matters for the exam

You should be able to classify a described migration scenario along three axes simultaneously — which push/pull category applies (economic, political, environmental, cultural), whether it is forced or voluntary, and whether it is internal or international — since a strong free-response answer usually needs at least two of these distinctions to fully characterize a real case. Be ready to cite a specific, named real-world example for each major category rather than a generic description; the Dust Bowl, the Syrian civil war, and the transatlantic slave trade are all high-value examples because each cleanly represents a distinct category (environmental push, political/forced international, and forced with essentially zero voluntary component, respectively). This lesson sets up the unit's closing topic directly: once you can explain why people move, the next and final lesson turns to what happens to the places they leave and the places they arrive — the real, measurable consequences of migration for both ends of the journey.