A federal system of government is a union of partially self-governing states or regions under a central government with powers usually assigned to each by a constitution. Neither the states nor the federal body acting alone can change the constitution.
The federal level handles maintenance of military forces, printing money, granting copyrights, maintaining a postal service, deciding monetary policy and other issues affecting the entire nation. The individual regions or states handle road and infrastructure maintenance, education policies and other local matters. In the United States, the balance of power has evolved dramatically overtime, with the flow of power trending from the states to the federal government. The basic powers of the U.S. federal government are listed in Article I, Section 8 of the U.S. Constitution.