From Wikipedia: National Origins Formula

 The policy overturned in the immigration law mentioned below.

- Click here for it.

The National Origins Formula was an American system of immigration quotas, used between 1921 and 1965, which restricted immigration on the basis of existing proportions of the population. It aimed to reduce the overall number of unskilled immigrants (especially from Southern Europe, Eastern Europe and Asia), to allow families to re-unite, and to prevent immigration from changing the ethnic distribution of the largely Protestant population of Northwestern European Americans.

The 1921 Emergency Quota Act restricted immigration to 3% of foreign-born persons of each nationality that resided in the United States in 1910.

The Immigration Act of 1924, also called the National Origins Act, provided that for three years the formula would change from 3% to 2% and the basis for the calculation would be the census of 1890 instead of that of 1910. After June 30, 1927, total immigration from all countries will be limited to 150,000, with allocations by country based upon national origins of inhabitants according to the census of 1920. The quota system applied only to non-Asian immigrants. It aimed to reduce the overall number of unskilled immigrants, to allow families to re-unite, and to prevent immigration from changing the ethnic distribution of the population. The 1924 Act also included the Asian Exclusion Act, which limited immigration to persons eligible for naturalization. As a result, East Asians and South Asians were effectively banned from immigrating. Africans were also subjected to severe restrictions.[1] Immigration from North and South America was not restricted.

The Immigration and Nationality Act of 1952 retained but relaxed the National Origins Formula. It modified the ratios to be based on the 1920 census and eliminated racial restrictions, but retained restrictions by national origin. President Harry Truman vetoed it because of its continued use of national quotas, but the Act was passed over his veto. The quotas were in addition to 600,000 refugees admitted from Europe after World War II.

The National Origins Formula was abolished by the Immigration and Nationality Act of 1965, which marked a significant change in American immigration policy. It replaced the system with two quotas for the Western and Eastern hemispheres.