Through the time of the Cultural Revolution China built defense facilities in remote regions away coastal areas, a network of factories was built in the interior of the country under the assumption that a full-scale war was likely. Many of China's largest defense-industrial facilities are located in the relatively remote interior, constituting the so-called "third line" of production from the days of the "People's War" doctrine. The location of these facilities has made it difficult for research and production facilities to sustain themselves under modern economic conditions. Starting in the early 1980's the government has worked to relocate some of these military research institutes and factories from these remote interior regions to urban areas. Due to the emphasis that China has placed on concealment of its special weapons capabilities, it is doubtful whether any other country, perhaps even including the United States, has identified all of China's special weapons related facilities.