Answer:
Studying economics enables us to understand past, future and current models, and apply them to societies, governments, businesses and individuals
The answer is to slowly readmit the confederate states to the union
The power of the national government will override the power of the states in term of conflict between the two powers.
Under supremacy clause, which written on article VI, clause 2 of the united states constitution, the law from the national government is considered as a supreme law that exist all across the nation and must not be crossed by any states.