In 1920, US needed immigrant labor to do hard jobs 2nd generation Americans just wouldn't do, per Congressman Rowe: We need men to work on farms, we need competent women to do housework, and in Europe there are men and women willing to do these jobs in America. US immigration quotas remained unchanged from 1921 to 1965

The US Immigration Act of 1921 established a "quota system that would last, virtually unchanged, until 1965"...  
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Dec. 10, 1920, "Congressional Debate on Immigration Restriction (1921) Excerpts"...history.hanover.edu (Hanover College, Indiana) 

"Congress imposed a literacy test and other restrictions on immigration during World War I. By 1921 many were arguing for even more stringent restrictions as a way of maintaining the purity of American culture as they understood it. The result of the debate excerpted below was to limit new immigrants to 3 percent of the nationalities represented in the census of 1910. In 1924 immigration was limited even further. -smv"

{17} MR. [FREDERICK W.] ROWE [R.-N.Y.]. Mr. Chairman... 

{18} The fact is that in this country we need laboring men and women of certain-classes. We are paying now in the city of New York for ordinary shovelers to dig trenches in which to lay a sewer or a water pipe from $4.50 to $6 a day. We are paying from $6 to $9 a-day for hod carriers. It is not because we have not plenty of men in this country. The fact is that our people of the second generation in this country will not carry a hod or dig a trench. We need the men on the farms. We have a great need in this country of competent women to do housework, and there are in Europe men who are willing to do this hard work in America and women who are capable and willing to do the housework. I believe in restrictions. I would have a very careful examination. I would not have it made under labor-union organizations. They represent only about one-ninth of the laboring men in this country. They should not have the power of saying who shall come and how the laws of this country shall be administered in respect to who is to be permitted to come into the Nation. I want to have restrictions. I think that for a limited time we might stop immigration in this country long enough so that Ellis Island may be made a proper place in which to receive all of the immigrants who desire to come into the country."...
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Added: "The Regulated Economy: A Historical Approach to Political Economy,"  Univ. of Chicago Press, Jan. 1994, National Bureau of Economic Research 

Chapter 7, "The political economy of immigration in the United States, 1890 to 1921," Claudia Goldin 

Introduction, 7.1: "With the passage of the Emergency Quota Act in May 1921 the era of open immigration to the United States came to an abrupt end.' The American policy of virtually unrestricted European immigration was transformed, almost overnight, to a quota system that would last, virtually unchanged, until 1965"...

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