The establishment of tight regulations on immigration in the U.S. was influenced by various factors, including xenophobia, economic anxiety, and the rise of nativist sentiments in the early 20th century. The post-World War I era saw increased fears about job competition and the cultural assimilation of immigrants, particularly those from Eastern and Southern Europe. Legislative efforts culminated in the Immigration Act of 1924, which imposed strict quotas based on national origins, significantly limiting immigration. This period marked a shift towards exclusionary policies that reflected broader societal tensions regarding immigration and the perceived threat to American identity.