International migration has more than tripled in size since 1960, rising from 77 million to almost 281 million by 2020. The costs of doing so declined:
First, the costs of movement. Air flights have reduced the cost, delays and uncertainties of travel. As more persons in developing countries gain more income, air travel is more affordable.
Second, the costs of settlement. As immigrant communities in destination countries increase in size, the ability of would-be and arriving migrants to to find housing, get jobs and fit in grows. This applies perhaps most to unauthorized migration – how to avoid deportation. But it also applies to legal immigration when channels such as refugee migration broaden. The Trump administration wants to stop the catch-and-release practices when people cross the Mexican border and then meet up with earlier migrants. This most recently has enabled unaccompanied minors to cross the southern border.
Third, the costs of keeping in touch with the host country. The most obvious improvement is in phone calls. It also includes air travel. Many immigrants today return for temporary visits. And consider remittances. Immigrant households in developed can probably better afford to share incomes in ways that can be used meaningfully in the country of origin. Methods of sending remittances have improved over the decades, and still are. African taxi drivers in Washington DC tell me they routinely back for stretches — their nuclear families live there.
Trump’s policy was essentially the increase the cost of migrating to the U.S. Just one example: it became much harder for spouses of H-1B workers to legally work.
Much of this is spelled out in Paul Collier, Exodus: How Migration is Changing our World.