What is the rule of federalism? How many levels? Do they have to be independent?

Federalism is a system of government in which entities such as states or provinces share power with a national government.
More: www.vocabulary.com/dictionary/federalism

The word is variously defined by other sources, and the actual operation in real life is likewise not the same in all cases. That is because when someone is given authority, he resents being told that he does not have endless authority.