US Immigration Act of 1921 sought to protect US standard of living. Immigration was restricted from 1921-1965 in part because American labor couldn't compete against cheap labor of Europe and maintain higher US standard of living (May 2, 1921, US Senate)

The US Immigration Act of 1921 established a "quota system that would last, virtually unchanged, until 1965."
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April 20, 1921, May 2, 1921, "Congressional Debate on Immigration Restriction (1921)," Excerpts from US House and Senate debates on immigration, 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"

"April 20, 1921, House of Representatives 

{1} MR. [LUCIAN WALTON] PARRISH [D-Tex.]. We should stop immigration entirely until such a time as we can amend our immigration laws and so write them that hereafter no one shall be admitted except he be in full sympathy with our Constitution and laws, willing to declare himself obedient to our flag, and willing to release himself form any obligations he may owe to the flag of the country from which he came. 

{2} It is time that we act now, because within a few short years the damage will have been done. The endless tide of immigration will have filled our country with a foreign and unsympathetic element. Those who are out of sympathy with our Constitution and the spirit of our Government will be here in large numbers, and the true spirit of Americanism left us by our fathers will gradually become poisoned by this uncertain element. 

{3} The time once was when we welcomed to our shores the oppressed and downtrodden people from all the world, but they came to us because of oppression at home and with the sincere purpose of making true and loyal American citizens, and in truth and in fact they did adapt themselves to our ways of thinking and contributed in a substantial sense to the progress and development that our civilization has made. But that time has passed now; new and strange conditions have arisen in the countries over there; new and strange doctrines are being taught. The Governments of the orient are being overturned and destroyed, and anarchy and bolshevism are threatening the very foundation of many of them and no one can foretell what the future will bring to many of those countries of the Old World now struggling with these problems."...  
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"May 2, 1921 
US Senate 

{10} MR. HEFLIN I do not intend to vote for any such proposition. I would like to shut for a time the immigration door. Thousands come here who never take the oath to support our Constitution and to become citizens of the United States. They pay allegiance to some other country while they live upon the substance of our own. They fill places that belong to the loyal wage-earning citizens of America. They preach a doctrine that is dangerous and deadly to our institutions. They are no of service whatever to our people. They constitute a menace and danger to us every day, and I can not understand the seeming indifference that some national lawmakers exhibit upon this serious subject. This very question of immigration is the most vital question that affects us to-day. 

{11} Senators, if we permit this thing to go on the day is coming when you can draw a line through the United States and ask the native stock to get on one side and the foreign born on the other and they will outnumber us. They will be in the majority....

{12} MR. WILLIAMS. The Senator speaks about the day coming when they will outnumber us. The day has already come, has it not, when they hold the balance of power and can decide a national election? 

{13} MR. HEFLIN That is true, absolutely true. They can get us divided on any great issue and get their forces in compact, concrete form and hold the balance of power and decide issues that affect the conduct and the life of the United States Government....

{14} Mr. President, I want to suggest to the Senator from Rhode Island and to others on the other side that I hear a great deal said about protecting American labor against the cheap labor of Europe; that the standard of living is so much higher here, 

{15} American labor can not compete with cheap labor of Europe. I could never understand why you would build a tariff wall between the products of the cheap labor of Europe and the United States and then throw the doors to America open to thousands of cheap European laborers to come here and compete with American labor. Yes, come here and compete with the loyal American citizen who has a wife and children to support. If you want to protect these men, protect them by keeping out those who work for starvation wages and spread their dangerous doctrines around the industrial establishments of our country, and take the places of our men, and get money that ought to be going into the pockets of the loyal wage earners of America. 

{16}...Senators, the time has come to stop this thing. We are seeking to keep these people out."...
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Added: The US Immigration Act of 1921 established a "quota system that would last, virtually unchanged, until 1965:"

"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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