After the end of the First World War and the 1920 Carinthian plebiscite, border changes led to changed traffic flows and the decline of the Rosen Valley Railway began. In October 1931, the last scheduled express train ran through the Rosen Valley, in 1933 the Krainische Industriegesellschaft closed its Feistritz works as a result of the Great Depression. During the Second World War, arms production at the Jungfer battery factory, which opened in Feistritz in 1939, led to a temporary traffic increase.