In fiscal year 2021, the share of the world population that the U.S. government permitted to immigrate legally to the United States was about 85 percent below its peak year of 1907 when 74 in 100,000 people became legal permanent residents of the United States. By 2021, that number had fallen to about 11 in 100,000—slightly lower than the 13 in 100,000 in 2019 or 16 in 100,000 in 2016.

Unlike those with various temporary statuses or no status, legal permanent residents are the only non‑U.S. citizens who may naturalize to become U.S. citizens. Measuring legal immigration as a share of the world’s population contextualizes potential immigrants’ actual opportunity to immigrate to the United States better than the absolute number of immigrants. No year has seen more than a fraction of a percent of the world’s population become U.S. legal permanent residents, but the share has declined, even as the desire to immigrate has increased.

Figure 1 shows the number of new legal permanent residents to the United States as a share of the non‑U.S. world population from 1840 to 2021. The lines after 1952 reflect the fact that some immigrants could adjust to legal permanent residence while already the United States. The share of “new arrivals” who enter from abroad as permanent residents fell even more dramatically from its high—nearly 95 percent below its peak in 1907.

During the era of mostly free immigration prior to 1925, legal immigration fluctuated wildly based on world events and the U.S. economy. But after visas were capped, an unnatural consistency developed at a low level. The one anomaly is in the period of 1989 to 1991 when the immigrants legalized by the 1986 amnesty adjusted to legal permanent residence. This experience was a small window into the demand that would exist if the United States had retained free immigration.

Table 1 ranks the years based on the share of the world population immigrating to the United States. Out of the 182 years, fiscal year 2021 ranks 122^nd in terms of total new legal permanent residents as a share of the world population and 167^th in terms of newly arriving legal permanent residents from abroad—which means only 15 years saw fewer new arrivals as a share of the world population than 2021.

If the United States had retained the same level of new legal permanent residents as a percentage of the world population as it saw during 1900 to 1924—the 25 years before the borders were closed—from 1925 to 2021, 160 million immigrants would have received permanent residence, compared to the 51 million who did. The level of legal immigration for 2000 to 2021 would be about 2.7 times the rate it actually was, permitting about 62 million immigrants as opposed to 22 million.

It’s reasonable to suppose that the actual rate would be higher than this, had the United States maintained its earlier policies. It certainly looks like the trend before World War I was upward from peak to peak. Transportation has also decreased significantly in price as well. The upshot is that the United States has extremely closed borders relative to what a reasonable person would expect under an even relatively open immigration system. This fact also explains why the country is experiencing so much more illegal immigration than in the past. When legal immigration is closed off, illegal immigration becomes most people’s only option.