Thälmann was also leader of the paramilitary Roter Frontkämpferbund, which was banned as extremist by the governing social democrats in 1929, and in 1932 he established Antifaschistische Aktion or Antifa, which concentrated its attacks on the recently formed social democratic paramilitary organization Iron Front. He was arrested by the Gestapo in 1933 and held in solitary confinement for eleven years; Stalin did not seek his release when he entered into the Molotov–Ribbentrop Pact with Germany, and Thälmann's party rival Walter Ulbricht ignored requests to plead on his behalf. Many of Thälmann's closest associates who had emigrated to the Soviet Union were executed during the Great Purge of the 1930s.