Federalism is a power-sharing arrangement between national and state governments where some powers are granted solely to the national government, some are reserved for state governments, and some are shared. American federalism involves multiple levels of government, including 50 states and thousands of local governments, that are related through the federal system outlined in the US Constitution. The Constitution makes the central government supreme in some matters but also makes clear that state governments have independent powers over issues within their own boundaries, uniting the levels of government only on issues concerning foreign nations.