Finnish immigrants have frequently been cited as the most politically radical ethnic group in America during the first three decades of the twentieth century, as indicated by the support they provided to the major left-wing organizations of the time. However, by 1945 this tendency was dissipating. Although political repression and nativist asperity were significant factors in undermining the left, they do not fully account for the downfall of leftist support. This article examines four other major factors: 1) the Bolshevization of the American left; 2) mass emigration to the Soviet Union; 3) the erosion of the ethnic community; and 4) the emergence of the “New American Society”.