Liebknecht was a member of the Independent Social Democratic Party of Germany ( USPD ) , opposed to the merger with the Communist Party of Germany and the joining of the Comintern but also to the reunification of the party with the Social Democratic Party of Germany , he continued the USPD as an independent party with Georg Ledebour until its merger into the Sozialistische Arbeiterpartei Deutschlands ( SAPD , Socialist Worker 's Party of Germany ) in 1931 .