Restriction of foreign immigration during the 1920s marked a significant change in U.S. policy. Immigration had soared in the late 19th century and peaked in the early 20th century. Between 1900 and 1915, for example, more than 13 million people came to the United States, with the preponderance from Southern and Eastern Europe. Many of these people were Jewish or Catholic, a fact that alarmed many older Americans who were predominately Anglo-Saxon and Protestant. Some resented the newcomers because they competed for low-wage jobs, others because the new immigrants maintained Old World customs, often lived in urban ethnic enclaves, and seemed to resist assimilation into the larger American culture.
As a result of this immigrant surge after World War I, nativist appeals intensified. A reorganized Ku Klux Klan emerged calling for "100-percent Americanism." Unlike the Klan of Reconstruction, the new Klan restricted its membership to native-born white Protestants, and campaigned against Catholics, Jews and immigrants as well as African Americans. By redefining its enemies, the Klan broadened its appeal to parts of the North and Midwest, and for a time, its membership swelled.
Anti-immigration sentiment was codified in a series of measures, culminating in the Immigration Quota Law of 1924 and a 1929 act. These laws limited the annual number of immigrants to 150,000, to be distributed among peoples of various nationalities in proportion to the number of their compatriots already in the United States in 1920. One result of these restrictions was to reduce the appeal of nativist organizations; the Great Depression of the 1930s also caused a sharp drop in immigration.
Source: U.S. Department of State