There were several events that led to the Red Scare, starting with Vladmir Lenin's ousting of the Russian government in 1917 with his Bolshevik Revolution. The United States sent troops to aid anti-communist Russians in overthrowing Lenin's Bolshevik party, but they were defeated.
In the United States, Soviet sympathizers formed the Communist Labor Party in 1919, which started the Red Scare in full force. Senator Alexander Palmer conducted illegal raids on U.S. residents, and hundreds of Russian immigrants were deported without due process. Palmer jump-started the creation of the FBI, which searched homes of suspected communist sympathizers without just cause and imprisoned many of them.