Definition - What does Federalism mean?
Federalism is a type of government in which there are both national and regional governments within a nation that both have unique powers and responsibilities. The American government is built on the principles of federalism. The Tenth Amendement to the Constitution lays out the terms of federalism within the American system of government.
Justipedia explains Federalism
The purpose of federalism in America is to diversify power between a number of different entities. This diversification is a hedge against one entity monopolizing power. It also allows both the federal and state governments to share the responsibility of governing the country. The federal government does things such as make treaties, decides on foreign policy, decides whether or not to wage wars, etc. State governments do things such as decide whether or not to ratify constitutional amendments, handles state law matters such as marriage, and other acts related to the state.