Hello! While the core of your question is fine, the title is a bit confrontational, as there are plenty of Communists who would take issue with it. We would ask that you reword the question with a more neutral title. You can decie on your own wording, or else I would suggest something along the lines of "How did the concept of communism found in Marx's writing evolve into the totalitarian strain that we see in the Communist regimes of the 20th century such as Stalinist USSR or Maoist China?" Additionally, "ELI5" is not something we like to see in titles, as it encourages rather poor answers from people.

Thanks for understanding!