In 1913-14, 1600 members of the Latvian Socialist Federation, which had cut earlier cut its ideological teeth on a Latvian-language Socialist Labor Party newspaper called Proletareets. made use of bloc voting and won control of the Massachusetts Socialist Party. The next year the center-right regulars regained control of the apparatus, causing the Latvians to seek a new institution for the exercise of their political voice. They established a new organization called the "Socialist Propaganda League" (SPL)— an organization with initials that are perhaps not accidentally a jumble of those of the SLP, as Paul Buhle has observed.
The Socialist Propaganda League of America was established was in 1915, apparently the product of one C.W. Fitzgerald of Beverly, MA. In the fall of 1915, Fitzgerald wrote and sent a leaflet to V.I. Ul'ianov (Lenin) of the Russian Social Democratic Workers Party— correspondence to which Lenin replied , outlining his views on the situation faced by the revolutionary socialist movement.
It was not until November of 1916 that any sort of broad-based organization was established. A November 26, 1916, meeting in Boston approved a first manifesto for the organization and established an official organ, called The Internationalist. According to the group's constitutionally stated objective, "The SPLA declares emphatically and will work uncompromisingly in the economic and political Þelds for industrial revolution to establish industrial democracy by the mass action of the working class." Initial editor of The Internationalist was Alfred S. Edwards, later an active member and District Organizer in the old CPA before leaving the organization for good in the Central Caucus split of late 1920.
In May of 1917, the name of The Internationalist was changed to The New International and Louis C. Fraina became the editor of the publication. Twelve issues were ultimately produced of the four page tabloid; press run was less than 1,000. The publication was terminated by the time the Boston-based and Fraina-edited weekly The Revolutionary Age began being issued in 1918. "The League is still in existence, but its paper is no longer published, since The Revolutionary Age expresses its policy," Fraina wrote in March 1919.
In January 1918, in the aftermath of the Bolshevik victory in Russia and the establishment of a Revolutionary Socialist regime there, the SPLA issue a second manifesto of the organization. The manifesto denounced "bourgeois democracy" as a "fraud" by means of which "Imperialism promotes the most brutal interests," advocated for "the unity of industrial action and Socialist politics," argued that "the revoluition of the proletariat annihilates the parliamentary regime and its state" and instead establishes a new form of government based upon workers ' councils that combine legislative and executive authority. The SPLA stated in this manifesto that "the organization is formed to work in the Socialist Party as well as independently of the party"— for "the revolutionary reorganzation of the American Socialist movement" both from within and without the SPA.
The Socialist Propaganda League called for a new revolutionary socialist International and was invited by name to attend the founding Congress of the Communist International in 1919. The organization was unable to send a representative in time to attend the gathering, however.
As a membership organization within the ranks of the Socialist Party of America, the Socialist Propaganda League of America was the direct lineal antecedent of the Left Wing Section of the Socialist Party and its governing National Council— the forerunner of the American Communist movement.