I've read many things specifically documenting Stalin's reign over the USSR, and even got perspectives from people who survived it
What is crazy is how I've read biographies from survivors of the Holocaust who became avid Marxists during their trauma, while Stalin was doing the exact same stuff to Christians. One guy who survived a USSR torture camp for Christians described his experiences in the camp (which i wont describe here bc kids are on this site), but to briefly sum it up, they were extremely underfed and forced to work in a very disgusting environment that was actively made to be as uncomfortable as possible for them. Eventually in describing it, he got to one point in time, and refused to go any further, claiming he had suffered worse than Christ (which makes no sense if your Christian). This was a pastor, and they broke him that bad (the USSR prided itself on its ability to break people).
I've read biographies from survivors of Hitler, Stalin, Lenin and Mao's reigns, and even the Japanese WW2 dictator (whose name i forgot)
Honestly just from reading biographies of people who grew up under Hitler and Mao, the similarities between the two are astonishing. Both manipulated the public by singling out a specific people group (for Hitler it was Jews, and for Mao it was "old school right wingers"), and they overthrew the government, got the youth involved by getting them to take pride in throwing out the old culture norms and replacing them with newer and better standards (Mao literally called the previous culture norms the four olds [which were four different classifications of old culture that needed to be thrown out]). Then they mass murdered their own people with full support from many of the public, and anyone who dissented, they used the army to intimidate them or flat out kill or persecute them. Thankfully for Germany, Hitler took 6 years to be defeated. China was not this fortunate, as Mao lived for over two decades after taking over, and during his reign, people viewed him as God and did not question him (because it usually resulted in death).