By the early 20th Century, the SLP was declining in numbers, with first the Social Democratic Party and then the Socialist Party of America becoming the leading leftist political force in America (as these splinter groups embraced capitalist reforms).
到20世纪初，社会主义劳工党党员数量正在下降，首先是社会民主党然后是美国社会党成为美国左派主要政治力量（这些分裂群体接受了在资本主义下的改革）。