Yes, the letter exists. Jack London's resignation letter from the Socialist Party is displayed in the museum on his estate. As Wikipedia states, the 1916 letter stated his disgust at the party's "lack of fire and fight", and its loss of emphasis on the class struggle. Not mentioned by Wikipedia is that Mr. London's letter closed by stating (paraphrase) that the prize jewels of justice, liberty, and self-determination cannot be simply handed over to all the lesser classes and races. They must be earned, and if they do not earn them, they will forever remain what they are; inferior classes and races. He signed it "Yours for the Revolution, Jack London".
Freedom Socialist Party was created in 1966.
Socialist Party of Vietnam ended in 1988.
There’s more than one answer. The Socialist Party of America was one.
the socialist party
The Socialist Labor Party was founded in 1891
Republican-Socialist Party ended in 1934.
Republican-Socialist Party was created in 1911.
Socialist Mexican Party was created in 1987.
Socialist Mexican Party ended in 1989.
Silesian Socialist Party was created in 1928.
Gabonese Socialist Party was created in 1992.
Cuban Socialist Party was created in 1899.