What are some historical examples of a morally corrupt government?

I need to compare three historical events to The Crucible/Salem With Trials. More specifically, I'm supposed to answer the following:

Is there danger in allowing those in power to determine what is morally right and wrong? Why?

My view is that there is potential danger within giving masses of power solely to any one person. Obviously, it does not always end with fatal or tragic consequences but there still are instances where this was the case. So I need examples that would support this idea.

My first thought was the Holocaust - how Hitler managed to exterminate millions of people. This is clearly morally wrong and yet he saw it as good. Hitler called it the Final Solution.

Another possibility is the genocide in Rwanda.

Are there any other examples you can think of? Any input would help. Especially if you can think of something from around the same time as the Salem With Trials.

Thank you!!