Dreiser depicted social strife and injustice throughout his early and midcareer, from Carrie's miserable shoe-factory job and Hurstwood's scabbing during a street car strike in Sister Carrie to his powerful rendering of the baleful effect of small-town class stratification and bias in An American Tragedy. By the late 1920s and early 1930s, however, like many other American writers and intellectuals, he began to be drawn more fully and personally into social and political issues, a tendency crystalized by the contrast offered by the seeming success of a Marxist economy in the Soviet Union and the failure of western capitalism signified by the Wall Street collapse and the onset of the Depression. By the mid-1930s he had plunged fully into an activist role, becoming a member of committees, a signer of declarations, and a writer of broadsides. He participated actively in almost all of the decade's famous causes, from the Harlan coal mine strike to the Free Tom Mooney campaign as well as in the efforts to secure justice for the Scottsboro Boys and victory for the Spanish Loyalists.

All these causes were embraced and exploited by the Communist Party, and thus it is not surprising that Dreiser was often identified during the final 15 years of his life as a communist sympathizer and that he formally joined the party in 1945. But Dreiser, as he made clear as early as his 1927 trip to the Soviet Union, had grave doubts about the applicability of a communist political system to the American scene. He thus cultivated as a solution to social injustice a vaguely defined idea of “Equity,” by which he appears to have meant a fairer distribution of a nation's wealth without recourse to the political authoritarianism of the Soviet system.

Dreiser's role as a principal spokesman for the literary left was severely damaged during the mid-1930s by the furor arising from the belief that he was anti-Semitic. The charge stemmed from his participation in a published “Editorial Conference” in the American Spectator for September 1933 and an exchange of letters between Dreiser and Hutchins Hapgood about the essay, which appeared in 1935. The matter received national attention, with American Jews on the Left in particular believing that they had been betrayed by a writer whom they assumed was a champion of the oppressed.