Researchers surveyed migration patterns and country migration policies since about 1960 and arrived at the following conclusions. Their conclusions explain succinctly American immigration, at both highly educated and low educated levels, including the high rate of illegal migration.
When pondering these observations also consider Paul Collier’s summary of what is driving migration – migration is less costly, and Trump tried to make it more costly.
(1) Long distance (intercontinental) migration has shifted from primarily Europeans leaving Europe to Africans, Latin America and Asians migrating between continents. 1960 about 85 percent of the foreign-born living in the US were from Europe (and Canada), this share had shrunk to 13 percent in 2016. The total person flow as a percentage of world population has remained fairly steady, between 2.7 and 3.3 percent of the world population. It’s the shift in key populations that gives the impression that long distance migration has grown relatively.
(2) Educated migrant flows have increased, in line with global education trends, while migration levels of persons with low formal education have persisted.
(3) Economic and human development in low-income societies tends to boost migration because it increases people’s capabilities and aspirations to migrate. Migration is an intrinsic part of broader development and social transformation processes.Most migration occurs between middle-income and high-income societies and most migrants from low-income countries belong to middle-income groups. Absolute poverty is associated with lower emigration levels, as resource constraints deprive people of the capability to emigrate.
(4) Emigration flows tend to tail off when a source country reaches the middle of global per capita income (purchasing power parity). (Go here.) The average among countries is about $18,000 PPP. This puts Mexico and Costa Rica at the cusp.
(5) Migration policies tend to work as filters rather than taps – not turning on or off the spigot, but filtering whom is allowed preferentially to immigrate.
(6) One way that migration can frustrate and overcome policies to restrict is the situation caused by reducing circulation; that is, reducing the free flow of migrants to a country and then returning, due to economic fluctuations in host and source countries. This is seen when the migration networks were already well in place and the economic pressures for migration are very strong. [This captures what happened between Mexico / Central America and the United States. Go here.]
(7) Migration policy becomes tortured in situations like the U.S. now, where there is fundamental mismatch between structural migration determinants—such as low-skilled labor demand in the absence of legal migration channels combined with weak workplace enforcement, or violence and conflict in the absence of asylum channels.
Article: Hein de Haas et al, International Migration: Trends, Determinants, and Policy Effects. Population and Development Review, October 2019