The majority of immigrants—at least in the United States—come for primarily economic reasons, to increase the level of opportunity for themselves and their families. So you might think that as countries become richer, people are more likely to stay put.
“The unmistakable pattern is that, for countries below something like $6,000–8,000 GDP per capita (at US prices), countries that get richer have more emigration,” he writes. “The threshold arrives at roughly the income per capita of Albania, Algeria, or El Salvador. But roughly half the countries on earth, and all the poorest ones, are below the threshold.”
Above the threshold, the trend reverses and higher GDP is associated with lower emigration.
Why is this the case?
Briefly: 1) Development is usually accompanied by a demographic transition that favors a corresponding mobility transition, 2) development means that more people can afford to emigrate, 3) development means that more people can access the information they need to emigrate, 4) development tends to disrupt economic structures that keep people immobile, 5) development shapes domestic inequality in ways that foster migration, and 6) development in country A means that people in country B are more likely to give visas to migrants from A.
It seems like a bit of a cruel paradox: The less economic opportunity there is within a country, the harder it is to leave it.