The Social Democratic Federation (SDF) was an American political party established as a result of a factional split in the Socialist Labor Party in 1889. Moving its headquarters through a succession of cities, the organization landed in Cleveland, Ohio, merging with the Social Democracy of America — forerunner of the Socialist Party of America — in the summer of 1897.
Together with the Central Labor Union of New York and other organizations, the SLP had formed a United Labor Party to compete in elections in the city and state of New York. In 1886 it invited Henry George to be its candidate for mayor of New York. In the campaign that followed George won 67,000 votes, second place. The next year, however, George's followers took full control of the party, ousting the SLP at its convention in Syracuse in August 1887. The socialist and a faction of the CLU then organized the Progressive Labor party that September. The election results for that year showed the ULP with 72,000 and the PLP with 5,000 votes.
The Social Democratic Federation (SDF) was established as Britain's first organised socialist political party by H. M. Hyndman, and had its first meeting on 7 June 1881. Those joining the SDF included William Morris, George Lansbury and Eleanor Marx. However, Friedrich Engels, Karl Marx's long-term collaborator, refused to support Hyndman's venture. Many of its early leading members had previously been active in the Manhood Suffrage League.
The SDF battled through defections of its right and left wings to other organizations during the first decade of the 20th Century before uniting with other radical groups to establish the Marxist British Socialist Party from 1911 until 1920 (not to be confused with the current Socialist Party of Great Britain founded in 1904, and the Socialist Party (England and Wales) founded in 1997).
The British Marxist movement effectively began in 1880 when a businessman named Henry M. Hyndman read Karl Marx's magnum opus Capital in French translation while crossing to America. Upon his return to London, Hyndman sought out Marx, then an exile living not far from his home. Hyndman, who had run for parliament earlier that year, decided to start a new political organization which he called the Democratic Federation and in June called its foundation convention, consisting of an assortment of radical grouplets and individuals.
The Social Democratic Federation of the United States of America (SDF) was a political party in the United States, formed in 1936 by the so-called "Old Guard" faction of the Socialist Party of America. The SDF later merged again with the Socialist Party in 1957 to form the Socialist Party-Social Democratic Federation (SP-SDF).
Social Democratic Federation leader Louis Waldman noted in his memoirs that while the official split of the Socialist Party that resulted in the creation of the Social Democratic Federation took place in 1936, "the crucial events occurred at the party's national convention in Detroit in 1934." It was at this national gathering that the ongoing factional war between a youthful "Militant" faction favoring aggressive advocacy of revolutionary tactics and joint action with the Communist Party won the day and pushed through a new Declaration of Principles, leading the SPA's right wing faction, known as the "Old Guard" to abandon the organization. Throughout the 1930s the Socialist Party had achieved moderate growth, it's paid membership returning to the 25,000 level and its candidate for President of the United States Norman Thomas polling nearly a million votes in the election of 1932.