Why is there only five volumes in the Soviet history series?

There are only five volumes in the Soviet history series, only five volumes have been published, and four volumes have not yet been published. Translating foreign historical books requires a lot of manpower and material resources, which involves the correctness of language and the authenticity of history. In order to provide readers with the real history of the Soviet Union, five books covering its important contents were first published. The history of the Soviet Union is a multi-volume history of the Soviet Union, which is divided into relatively independent historical stages, namely, the Russian revolution, the civil war, the new economic policy period, the establishment of Stalin's model, the Great Patriotic War, the post-war Stalin period, Khrushchev's ten years, Brezhnev's eighteen years, Gorbachev's reform and the disintegration of the Soviet Union.