Final answer:
The selection criteria for immigration until 1961 was based on the National Origin Formula, which used numerical limits and a quota system to restrict immigration from certain countries.
Step-by-step explanation:
The selection criteria for immigration until 1961 was based on the National Origin Formula, which was enacted in 1921. This formula set numerical limits on European immigration and used a quota system based on the residents from each country as counted in the 1890 or 1910 census. The purpose of this formula was to preserve the ideal of American homogeneity and restrict immigration from certain countries, particularly those in southern and eastern Europe. However, in 1965, the Immigration and Nationality Act was passed, which ended the discriminatory practice and allowed immigrants from a wider range of countries to enter the U.S.