 After the revolution in Russia in 1917 , the communist movement gradually gained footholds in many countries around the world . In Europe and the US , communist parties were formed , generally allied with trade union and labor causes . During the First Red Scare of 1919 – 1920 , many Americans were fearful that Bolshevism and anarchism would lead to disruption within the US . In the late 1930s , state and federal legislatures passed laws designed to expose communists , including laws requiring loyalty oaths , and laws requiring communists to register with the government . Even the American Civil Liberties Union ( ACLU ) , a free @-@ speech advocacy organization , passed a resolution in 1939 expelling communists from its leadership ranks . 
