The First Red Scare occurred in 1919-1920 after the fear of Bolshevik influence when communism took over Russia. Many Americans were afraid that communism could spread to the United States and threaten the democratic values of the nation once the United States no longer had to concentrate its efforts on winning World War I. The mass immigration of Southern and Eastern Europeans to the U.S. and labor unrest in the late 1910s, including the Great Steel Strike of 1919, fueled this fear. Due to the First Red Care, thousands of people were arrested, and hundreds of people were deported and labeled as "communists" during the scare.
Irrational paranoia was not rooted in the first Red Scare that started a century ago. There was an unambiguous purpose for the government agencies which carried out the arrests: to kill the radical left in the United States.