I think it was the communism - it was a really bad economic system that was so out of touch with the reality of human beings and the past thousand years that people had no other choice but to engage in corruption (bypassing the system).
There's the communist revolution, which gave power to people who were not fit to wield it. There's the dekulakization, which liquidated millions of people who knew what they were doing. Then there's the forced collectivisation...
