Nativists not only objected to the numbers of immigrants, but also to the potential impact newcomers would have on “traditional American values”. During the late nineteenth and early twentieth century, nativist groups such as the American Protective Association, the Immigration Restriction League, and the Ku Klux Klan buttressed their demands for restriction with "scientific" arguments. They often employed eugenics to prove the "inferiority" of Asians and "new" immigrants from southern and eastern Europe, mostly Catholics and Jews. Even academics, clerics, and intellectuals feared the mixing of old stock Europeans and Americans with the so-called "backward races" of southern and eastern Europe -- a condition, they believed, that could only lead to "race suicide" and "reversion" to a more primitive state.

Cultural assimilation, also known as Americanization, was a less drastic means of dealing with the numerous ethnic enclaves in American cities. While restrictionists rejected immigrants entirely, assimilationists believed that immigrants could adapt to the American way of life. The Immigration Protective Association, the International Ladies Garment Workers Union, the Amalgamated Clothing and Textile Workers Union, and representatives of the settlement house movement aimed at helping immigrants shed or at least diminish their Old World cultural roots and become "Americans."