One hundred years ago this month, President Calvin Coolidge signed the Immigration Act of 1924. Passed by large majorities in the House and Senate, the law overturned the system of mostly free immigration that had prevailed for the previous century and a half, transforming America from a collection of English colonies hugging the Atlantic Coast into a mighty, continent-spanning nation of immigrants. In place of the old system, Congress created strict limits on the number of newcomers who could immigrate to America and imposed an annual global quota of just 165,000.

For the first century and a half of American history, “illegal immigration” was a nonexistent concept. Individual foreigners could be excluded by law for specific reasons — for example, being guilty of crimes of “moral turpitude,” having a contagious disease, or being a known anarchist. Immigrants were not admitted if they were likely to become a “public charge,” dependent on government assistance. Otherwise, almost anyone who could get to America was welcome to become a legal permanent resident.

The 1924 law turned that system upside down. For the first time, all prospective immigrants were required to obtain an immigrant visa before entering the country. Migrants to America without such a visa lacked legal status and could be deported.

It was a terrible law, steeped in racism and the quack science of eugenics. Its quotas were heavily tilted in favor of immigrants from Great Britain, Ireland, and Northern Europe. By contrast, immigrants from Asia were almost wholly barred, while Russians, Poles, Italians, Jews, and Greeks — deemed by progressive elites of the day to be genetically inferior and incapable of assimilating with Anglo-Saxons — were reduced to a trickle. The new legislation was popular, supported by prominent scientists, leading media voices, the Ku Klux Klan, and the American Federation of Labor, all of whom resented or feared the waves of immigrants who had been surging into the country since the 1870s.

Among the admirers of the 1924 Immigration Act was Adolf Hitler, who praised the new US policy in “Mein Kampf.” In November 1933, the National Socialist Monthly, a Nazi Party journal, saluted Americans for rejecting the “melting pot” approach to immigration and “put[ting] a check on bastardization through draconian immigration law.” Among its other effects, the 1924 law ensured that America’s doors would remain firmly closed to Jews and other Europeans desperate to flee the Holocaust, with terrifying lethal results.

There is a popular misconception that the 1924 law was undone by the Immigration and Nationality Act of 1965. In reality, as the Cato Institute’s David J. Bier has written, every essential feature of our current system dates back to 1924: “a presumption against legal immigration, a low overall cap, country-by-country caps, and a preference for family unity.”

Above all, the system established in 1924, by making it impossible for most would-be immigrants to enter the United States legally, guaranteed a steady stream of illegal immigration. American freedom and the American economy are such powerful lures that even the high hurdles of our immigration laws are not enough to dissuade all those who seek to improve their lives by becoming US residents. And while millions of undocumented border crossers have been deported over the years, an estimated 11 million others have settled in the United States, becoming productive workers, taxpayers, homeowners, parents, and entrepreneurs.

What has America gained by making it so difficult for peaceful and industrious foreigners to immigrate lawfully?

If not for the slamming of the gates in 1924, it is likely that America’s population would be double what it is today. That would mean, as Bier notes, that “the United States would not have lost nearly as much diplomatic, social, and market influence to China and other countries in recent years if its economy and consumer base were twice as large as they are now.” With a larger population, America would have a larger, richer, and more productive economy. Since immigration tends to be a formidable engine of economic growth and innovation, a century of more open immigration would have made the United States wealthier, stronger, and more advanced. It would have enlarged the level of freedom enjoyed by US citizens. It would have lifted hundreds of millions of people worldwide out of poverty or liberated them from tyranny and oppression. And it would have eliminated our endless furor over “illegal immigration.”

One of President Coolidge’s favorite maxims was that “it is much more important to kill bad bills than to pass good ones.” It is ironic that he of all people should have signed one of the worst bills of the 20th century. For 100 years, the Immigration Act of 1924 has been a blight on American society. Will it take another 100 years to uproot that ugly law?