The historical period that came to be known as the McCarthy era began well before Joseph McCarthy's own involvement in it. Many factors contributed to McCarthyism, some of them with roots in the First Red Scare (1917–20), inspired by communism's emergence as a recognized political force and widespread social disruption in the United States related to unionizing and anarchist activities. Owing in part to its success in organizing labor unions and its early opposition to fascism, and offering an alternative to the ills of capitalism during the Great Depression, the Communist Party of the United States increased its membership through the 1930s, reaching a peak of about 75,000 members in 1940–41. While the United States was engaged in World War II and allied with the Soviet Union, the issue of anti-communism was largely muted. With the end of World War II, the Cold War began almost immediately, as the Soviet Union installed communist puppet régimes in areas it had occupied across Central and Eastern Europe. The United States backed anti-communist forces in Greece and China.