What is federalisum? what does it do?

The United States government is based on federalism. Federalism is a method of government that allows two or more entities to share control over the same geographic region. Each person in the United States is subject to the laws of that city, county, state and our federal government.

In a federalist government, the power is divided between the national government and other governmental units. In the U.S., this means the power is divided between our federal government and our state and local governments.