Daniel De Leon joined the Socialist Labor Party of America in 1890. During the period that followed, he increasingly defined its political course and this resulted in a decisive shift to the left.
De Leon was also a co-founder of the Industrial Workers of the World and was active in the union until it split in 1908. In the wake of clashes with the IWW’s radical wing, De Leonism developed into an independent political current and to a Marxist form of syndicalism that strove for the control and management of a socialist economy through the trade unions. De Leon died in 1914; his followers later rejected Soviet-style “real socialism”.