Why was nativism present in the 1920s and who was it directed at?

The 1920s was an era of much positive social change (women getting the vote; more middle class young people attending college; black artists, poets, and playwrights leading the "Harlem Renaissance"; new technologies like radio bringing news, education, and entertainment to millions, etc). But it was also an era when the Ku Klux Klan experienced a dramatic increase in influence, and there was also an increase in prejudice directed at Jews, blacks, and immigrants. There was no one person leading the charge: a number of anti-immigrant groups surfaced, of which the KKK was the best known and best organized (they even had their own radio station to spread their message of hate for those who were not white and Christian).

But sad to say, anti-Jewish or anti-black bigotry was embedded in the popular culture. America was still segregated, and despite the advances many blacks experienced up North or the praise the members of the artistic community received during the Harlem Renaissance, minority rights were very much restricted throughout the country, and the Ku Klux Klan was able to capitalize on fear of upwardly mobile Negroes (as they were then called) gaining more power in society. The same was true about Jews-- many colleges, including Harvard and Dartmouth, put in quotas so that their schools would not have "too many Jews." While many Jews succeeded in certain professions like entertainment or science, they were still barred from numerous other occupations. And fear of "too many immigrants" led to restrictive policies and quotas on who could come to America. Nativism, the belief that only the "native born" should be allowed to live in the USA, or that only native born (white Protestant) Americans should hold power, was alive and well, one very negative aspect of an otherwise positive decade.