Common government mistakes?

This year I'm taking world history, and for our final exam we are to write an essay about whether or not, throughout history after the fall of Rome, governments learn from their own/ other governments' mistakes and provide three examples. I am saying that they do not, so far two examples I have are granting too much power to one leader (monarchy/empire/dictatorship) and not tolerating diverse religions. I need a third (that can apply to multiple civilizations), any ideas?