In spite of its bustling life, the excitement for so many new innovations, the increased quality of life in many parts of the country and the new freedom many people enjoyed, the Twenties was also a time of great (sometimes irrational) fear and anxiety.
There are many reasons why American society as a whole felt insecure.
The very fast change of ways of life and morals foreshadows an unpredictable future that, if it was exciting for some (especially young people) it was scary for many. Cities were fast growing, changing their faces both in terms of environment and population. There was a new way to do nearly everything, and people had to adjust to it whether they felt comfortable about it or not.
In addition to this, many things were happening outside the US that forced their way in.
World War I broke out in Europe, and even if America tried to stay out of it for a long time, she was eventually forced to enter the conflict, sending her young men across the ocean never to see many of them return. This left an undercurrent of insecurity in all that generation that sparked (some say) the demand for life and fun in the Twenties but implanted insecurity deep down.
Right after the war ended, Revolution broke out in Russia, bringing about a communist regime. The idea that that ideology could reach across the ocean and destroy the right to ownership so important to American society created an hysteria (the Red Scare) that, though largely unfounded, was nonetheless powerful and informed many sections of American life.
Prohibition created the possibility for many gangs and gangsters to raise an unbelievable racket that brought a different war in the streets of the major cities. New immigrants willing to work for substandard wages and to brake union strikes flooded into cities across the nation.
There seemed to be a common element to much of this: the causes of much of this insecurity were imported. They came from outside, carried over by the crowds of people coming from across the oceans, especially from Europe. So there was a solution: the gates must be closed.
Up to the end of the XIX century, immigration policy had been quite liberal. The young nation was growing fast and it needed people and workers, so basically anyone would be let in, as long as they were wiling to become regular Americans as everyone else.
But in the Twenties, one third of the population had immigrated or was born to immigrated parents. They were still so new to America, they could hardly be considered Americans yet. Most of time, they still practiced their own original culture. They may bring in ideas from their original countries.
The first Immigration Act was passed in 1917, right after America entered WWI and it restricted access to only people who could read and write in English or any other language.
After the race riots of the summer 1919, the wave of strikes that smelt of communism in 1919-1920 and the beginning of the “crime wave” brought about by ethnic gangs, Congress passed an emergency immigration act in 1921. For the first time, this act stated a maximum quota to immigration from Europe to 3%of the number of people from any single nationality as they appeared in the 1910 census.
But the master law was the Immigration Act of 1924, which brought down the percentage to 2% of any single nationality as it appeared in the census of 1880.
That left only a trickle of immigration from Northern Europe. The gates were closed.
The Social Studies Help Center – To what extent was American xenophibic in the 1920s?
Office of the Historian – The Immigration Act of 1924 (The Johnson-Reed Act)
Immigration in America – The Immigration Act of 1924BBC – What was the Red Scare?
The Immigration Act of 1924 (pdf)
Perrish, Michael E., Anxious Decades: America in Prosperity and Depression, 1920-1941. W.W. Norton & Co. Inc., New York, 1992