5 of May 19, 1921), was formulated mainly in response to the large influx of Southern and Eastern Europeans and restricted their immigration to the United States.

[1] The Immigration Act of 1924 reduced the quota to 2% of countries' representation in the 1890 census, when a fairly small percentage of the population was from the regions some regarded as less than desirable.

[citation needed] In 1921, there was a drastic reduction in immigration levels from other countries, principally Southern and Eastern Europe.

The use of the National Origins Formula continued until it was replaced by the Immigration and Nationality Act of 1965, which introduced a system of preferences, based on immigrants' skills and family relationships with US citizens or US residents.

The 1922 and 1925 systems based on dated census records of the foreign-born population were intended as temporary measures, and were replaced by the 1924 Act's National Origins Formula based on the 1920 Census of the total U.S. population, effective July 1, 1929.