 After a month of training by the Cheka in subversive activities, the Hungarian Communist Party (KMP) sent Nagy along with 277 other Hungarian communists to Hungary in April 1921 to build up an underground conspiratorial network in a country where the Communist Party had been banned since 1919.Nagy reached Kaposvár in late May 1921.Upon arrival, he joined the Social Democratic Party of Hungary (MSZDP).