There's a lot of information in the book Socialism in Power by Roland Boer, specifically chapters 4 through 6 deal with the Soviet Union of Lenin and Stalin. And chapter 7 deals with democracy in the DPRK.
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I also came to recommend Roland Boer! "Socialism with Chinese Characteristics" touches on the USSR (more than touches actually, it does have some in depth explanations) and there is quite a lot about Stalin, democracy in one party states, and Democratic Centralism that you'll find relevant to you curiosity, OP.