Federalism is a system of government where power is shared between national and state governments. The US Constitution divides powers between the federal and state governments. Over time, the division of power has shifted from a "dual federalism" model, where each level remained supreme in its own sphere, to a "cooperative federalism" model where powers are shared. The national government provides grants to states and local governments to fund programs, though these grants come with requirements, or "strings attached." Both advantages and disadvantages exist to having multiple levels of government in a federal system.