@kiba, pjscott is correct. But what makes countries rich is not laws. It's natural resources. Either having them, or having control over them, even if they are in another country. Give it some thought. Apply the idea to some sample countries. You might revise your thesis.

Form of government might be a red herring. Corruption and injustice might be tied to people and culture, not simply to form of government. Think about it.