I think your teacher may really mean the 1920s. The real relevance was during that time period.
Many Americans stood firmly against immigration during the 1920s. Although nativist groups such as the Know-Nothings and the American Protective Association had been around since the 1800s, Congress had rarely given in to these groups and had done little to stem the flow of immigrants into the United States. All this changed in 1921, however, when Congress passed the Emergency Quota Act in response to the unceasing wave of new immigrants into the country.
As its name implied, the Emergency Quota Act established a specific, unalterable number of immigrants from each country who would be allowed to enter the United States every year. Specifically, each immigrant’s country of origin could send only 3 percent of the number of persons from that country who were living in the United States in 1910; all other immigrants would be shipped back to the countries from which they came. Three years later, Congress repealed the Emergency Quota Act and passed the Immigration Act of 1924, which changed each foreign country’s annual immigrant quota to 2 percent of the number of persons from that country who were living in the United States in 1890.
In general, immigration had been a boon to the rapidly expanding U.S. economy during the nineteenth century, as immigrants from Ireland, Germany, and southern Europe had provided invaluable labor in city factories. The Emergency Quota Act and the Immigration Act of 1924, however, effectively slammed the door shut on the bulk of new immigrants. The effect was enormous and reduced the number of yearly arrivals by about 500,000 annually—blocking almost all southern and eastern Europeans. The number of immigrants from northern and western Europe, on the other hand, remained relatively steady, between 150,000 and 200,000 per year. These laws implemented the first severe limitations on immigration after nearly a century without much restriction.
Congress passed these new restrictive immigration laws in part because of the growing fear of socialism that was spreading through southern and eastern Europe. After Russia collapsed to communism in the Russian Revolution of 1917, panic swept across the United States. In the Red Scare of 1919–1920, Americans became suspicious that they might fall victim to a communist plot to take over the country. The two main methods that workers’ unions used to create fair labor agreements—striking and collective bargaining—came to be seen as tools of socialists and anarchists. As a result, labor unions were frowned upon and dwindled in number and size. Several hundred Americans who affiliated with the Communist and Socialist parties were arrested, as were labor organizers and others who criticized the U.S. government.
The Socialist Party’s growing membership in the United States was also perceived as a threat, especially since labor organizer Eugene V. Debs received nearly a million popular votes in the presidential election of 1920. Even though the Red Scare eventually subsided, the fear of socialism and communism in the United States never truly went away. It would eventually resurface in the 1950s and throughout the Cold War.
****edit***
That's because I got a work related phone call and couldn't finish my thoughts. Sorry, but real life IS more important than Yahoo Answers. Finished now.