The socialist journalist Willi Eichler succeeded Nelson as president of the ISK after his death. Eichler and Specht would both sign the 1932 "Urgent Call for Unity" ("Dringender Appell für die Einheit") in the ISK's official newspaper, "Der Funke". It called for Germany's Social Democratic Party (SPD) and Communist Party (KPD) to create a left-wing united front in order to thwart the Nazis. After the Nazi's defeat in 1945, the ISK was merged with the SPD with the agreement met on 10 December 1945, between the chairman of the ISK (Will Eichler) and chairman of the SPD (Kurt Schumacher). However, the ISK continued to be active in the resistance against Nazism. A British affiliate of the ISK was created (lasted from the 1920s to the 1950s) in the United Kingdom called the Socialist Vanguard Group.