The primary factor that led to the Red Scare in the U.S. during the 1920s was the fear of communism following the Russian Revolution of 1917. Amid rising tensions globally, American society experienced anxiety about socialist and anarchist movements, which included labor strikes and unrest. The Bolshevik Revolution stirred concerns that a similar uprising could occur in the U.S. This anxiety was exacerbated by high-profile events such as the Palmer Raids, where government officials arrested and deported immigrants suspected of radical activities, reflecting the pervasive fear of a domestic communist threat that defined the Red Scare era.