Thompson left the Socialist Party owing to its opposition to World War I and thereafter participated in other liberal political organizations, including the Committee of 48 and his own group, the National Public Ownership League.

Carl D. Thompson was born on March 24, 1870, in Berlin, Michigan, a small town on the shore of Lake Erie in the southeastern corner of the state.

In 1900 he was minister of the Prospect Street Congregational Church in Elgin, Illinois, and in regular contact with Christian Socialist J. Stitt Wilson.

Thompson also ran as the SPA's candidate for US Congress from Illinois's 7th congressional district against incumbent Democrat Frank Buchanan in 1914.

[9] Upon termination of the SPA's Information Department, he remained in Illinois and went to work as head of the party's National Lecture Bureau.

In 1916, Thompson ran a tightly fought campaign against former United Mine Workers Union official Adolph Germer for the position of National Executive Secretary of the Socialist Party.

[10] As this political situation became clear in the summer of 1918, Thompson and his co-thinkers on the Socialist Party's right wing admitted defeat and left the ranks of the organization.