Final answer:
In response to nativist fears, Congress passed the Emergency Quota Act of 1921 and the National Origins Act of 1924 to restrict immigration, especially from Southern and Eastern Europe and Asia. These acts established quotas based on old census data, which favored Western Europeans. It took until 1965 for the U.S. to revise its immigration policies to be more inclusive.
Step-by-step explanation:
U.S. Immigration Legislation After World War I
Following World War I, in response to nativist fears, Congress enacted several laws to restrict immigration. The Emergency Quota Act of 1921 was the first such piece of legislation, imposing yearly limits on the number of immigrants at 350,000 and setting quotas based on nationalities as a percentage of the U.S. census figures from 1910.
This act, along with the National Origins Act of 1924, significantly curtailed immigration from Southern and Eastern Europe, and outright excluded Japanese immigrants. The 1924 Act set quotas based on the 1890 census, favoring immigrants from Western Europe and effectively restricting others, in an effort to 'preserve the ideal of American homogeneity'.
Furthermore, agitation from nativist groups led to the establishment of literacy tests and the infamous Chinese Exclusion Act. An underlying theme during this period was the balancing act between nativist impulses and America's self-image as a land of opportunity, as well as economic needs, particularly in relation to labor demands.
It wouldn't be until the Immigration and Nationality Act of 1965 that a more equal and humane approach to immigration would be realized.
This Act overturned the biases of the 1920s' policies, lifting restrictions on immigration from Asia in particular and prioritizing family reunification and skilled immigrants. As a result, it set the stage for the formation of diverse immigrant communities in subsequent decades.