What events in Europe lead some Americans to fear foreigners and foreign ideas after World War 1?

After World War I, several events in Europe heightened American fears of foreigners and foreign ideas. The Russian Revolution of 1917, which established a communist government, fueled anxieties about the spread of communism and radical ideologies. Additionally, the rise of fascist movements in Italy and other parts of Europe raised concerns about political extremism. Coupled with economic instability and social unrest in the U.S., these developments fostered a climate of suspicion towards immigrants and foreign influence, leading to increased nativism and isolationist sentiments.