The border has never been more closed than it is today, thanks to the Biden administration’s decision to extend Title 42, a public-health-related immigration restriction put in place in March 2020 by President Donald Trump amid the coronavirus pandemic. Yet right-wing critics of President Biden assert that he is somehow encouraging border crossing by being insufficiently tough on immigration enforcement.

The roots of Biden’s policy headache lay in an immigration system built primarily around restricting the ability to migrate. More than that, the system was designed specifically to keep out people deemed racially undesirable. In fact, Wednesday marks 100 years since the enactment of one of the most restrictive immigration laws in U.S. history, one that inaugurated the contemporary era of immigration crises and expanded border security.

On May 19, 1921, President Warren G. Harding signed the Emergency Quota Act into law, ending the era of open immigration to the United States from Europe. The immigration quotas in the law were meant to be a temporary measure to slow immigration after World War I. The legislation and a subsequent 1924 law had a massive impact: From 1880 through 1920, 23.5 million people immigrated to the United States, but between 1921 and 1965 only 6 million more would come.

The 1921 Emergency Quota Act didn’t materialize out of nowhere; it built on previous immigration restrictions, often targeting people from Asia. The United States’ first federal immigration laws, the Page Act of 1875 and the Chinese Exclusion Act of 1882, banned Chinese immigrants. These were followed by the Gentlemen’s Agreement of 1907, which banned Japanese immigrants, and the creation of what was deemed an “Asiatic Barred Zone” in 1917 during World War I.

Even after the United States began restricting migration from Asia, the vast majority of immigrants from Europe remained free to come. However, as people arriving from Southern and Eastern Europe began to outpace those coming from Northern Europe, critics proposed additional restrictions to curtail immigration.

The reason for their concern? Emerging ideas about race science and genetics that were driving the development of the field of “eugenics.” Newly arriving immigrants from Southern and Eastern Europe were considered suspect because of questions of ethnicity and race. On the Senate floor in 1896, Sen. Henry Cabot Lodge (R-Mass.) spoke out against “a great and perilous change in the very fabric of our race.”