Asian Exclusion Act

The Immigration Act of 1924, or Johnson–Reed Act, including the National Origins Act, and Asian Exclusion Act (Pub.L. 68–139, 43 Stat. 153, enacted May 26, 1924), was a United States federal law that limited the annual number of immigrants who could be admitted from any country to 2% of the number of people from that country who were already living in the United States as of the 1890 census, down from the 3% cap set by the Emergency Quota Act of 1921, which used the Census of 1910. The law was primarily aimed at further restricting immigration of Southern Europeans and Eastern Europeans, especially Italians and Eastern European Jews. In addition, it severely restricted the immigration of Africans and outright banned the immigration of Arabs and Asians. According to the U.S. Department of State Office of the Historian the purpose of the act was "to preserve the ideal of American homogeneity". But though the Act aimed at preserving American racial homogeneity, it set no limits on immigration from other countries of the Americas. Congressional opposition was minimal.

The Immigration Act made permanent the basic limitations on immigration into the United States established in 1921 and modified the National Origins Formula established then. In conjunction with the Immigration Act of 1917, it governed American immigration policy until the passage of the Immigration and Nationality Act of 1952, which revised it completely.

...
Wikipedia