What events in Europe led some Americans to fear foreigners and foreign ideas after world was one?

After World War I, several events in Europe contributed to American fears of foreigners and foreign ideas, including the rise of communism and the Bolshevik Revolution in Russia. The spread of radical political movements, labor strikes, and social unrest fueled concerns about the influence of immigrants and leftist ideologies in the U.S. Additionally, the Red Scare of 1919-1920 heightened anxieties about potential subversion and internal threats, leading to increased xenophobia and a backlash against immigrants, particularly from Eastern and Southern Europe. This culminated in restrictive Immigration policies and a general climate of suspicion toward foreign influences.