The word "federalism," which names one of the most important concepts in the United States political system, is not even mentioned in the U. S. Constitution. The word "federal" denotes a form of government in which power is distributed between a central authority and a number of constituent territorial units. In the United States the "central authority" is the federal government; the "constituent territorial units" are the state governments. Under the U.S. Constitution, those powers that are not specifically granted to the national government are presumed to be retained by state governments. Hence, state governments, like the federal government, have their own spheres of jurisdiction.

We Americans are actually citizens of two governments, national and state, each of which makes law and sets policies that affect our daily lives. This complex system of multiple levels and divisions of government enables many levels of civic participation and many ways to serve human needs; yet it is difficult to understand and sometimes inefficient. It has also served to enable some Americans to deny other people in the nation of their fundamental rights (e.g., slavery and Jim Crow laws). The framers of the Constitution chose this system because they believed that although a strong federal government is necessary for certain purposes, they also were committed to strong state governments, which could more effectively address problems of a local nature. They chose the federal system as one way to limit the powers for government in order to help assure that citizens retain their fundamental rights.

Throughout United States history, citizens have debated and even fought, as in our Civil War, over how those powers should be divided, some holding that states are better able than the federal government to respond to most public policy issues, whereas others take the opposite position. The federal system has changed over time. Early in the history of the republic, the federal government was small and had limited powers. Over time, the powers of the federal government expanded considerably, especially when crises occurred that affect the entire nation or when problems occur that cry out for a national solution. Federal power has expanded especially during times of war.

One event that led to the expansion of federal power was the Great Depression, when it became obvious that the problems in one state were affected by problems in the other states and the consequences for people were horrendous. The administration of Franklin Delano Roosevelt responded with many programs, which had the result of expanding federal powers considerably. Not all Americans have approved of such changes in the federal system. In the area of civil rights in the 1950s and 1960s especially there were fierce debates over whether the federal or state governments should have the most authority. Today, such debates continue in that area, as well as with regard to how to address poverty, environmental problems, problems in education, and inequities of all sorts.