Since the late 1930s, Soviet historiography treated the party line and reality as one and the same.[13] As such, if it was a science, it was a science in service of a specific political and ideological agenda, commonly employing historical revisionism.[14] In the 1930s, historic 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.[15]