That criticism stems from the fact that in the Soviet Union, science was far from independent. Since the late 1930s, Soviet historiography treated the party line and reality as one and the same. As such, if it was a science, it was a science in service of a specific political and ideological agenda, commonly employing historical revisionism. In the 1930s, historical archives were closed and original research was severely restricted. Historians were required to pepper their works with references—appropriate or not—to Stalin and other "Marxist–Leninist classics", and to pass judgment—as prescribed by the Party—on pre-revolution historic Russian figures. Nikita Khrushchev commented that "Historians are dangerous and capable of turning everything upside down. They have to be watched."
