You certainly could qualify those leaders you mentioned as a "piece of shit", including Mussolini and Hitler. It's a qualification based on emotion instead of rational analysis. "The old guy" of Zimbabwe is commonly known as Mugabe (his family name). Idi Amin is a former leader of Uganda.

You mix bananas and apples, another problem. African leaders like Mugabe and Idi Amin follow the lines of tribalism in their lines of politics, which is a totally different thing and cannot be compared to what leaders like Stalin, Lenin, Hitler or Mussolini did.

To prevent such atrocities happening again, people must learn from the lessons of history. This can only be done by rational analysis in determining the factors of why such things could happen. One of those factors is power structure. All those "pieces of shit" you cared to list in your post were dictators. Folks like Trump may also pave the way for future dictators. Would you also call him a "piece of shit"?

Which country leaders, in history and now, are the equivalent to this piece of shit?