The main reason the South seceded from the Union is that it felt that the states should have greater control over the direction of their laws and should be less subservient to the federal government. The majority of Southerners in this time period identified more with their state than with the nation. So, the Civil War can be seen as a conflict over the interpretation of American Federalism. The South felt that the system of Federalism should divide powers more equally between the state and national governments, and the Union felt otherwise. This disagreement was effectively resolved (legally speaking) with the passage of the Fourteenth Amendment, which outlined the requirements for states to abide by national laws.

For the first one hundred and fifty years of American political history, the country essentially operated under Dual Federalism, also called "Layer-cake Federalism." This involves a clear delineation of powers reserved for national governments, state governments, and local governments. During the Great Depression, the power of the Federal government grew dramatically, and the United States' federalism system began to appear more like Cooperative Federalism, also called "Marble-cake Federalism." In Marble-cake Federalism, national, state, and local governments work together cooperatively to tackle problems and pass laws.

Nullification declares that the states have the right to declare any federal law unconstitutional or illegal and choose to ignore it within the state itself. This position was championed particularly by Thomas Jefferson as is the central point of the Kentucky and Virginia Resolutions. Because nullification involves the repudiation of the ultimate authority of the national government, it can be understood as a rejection of the Supremacy Clause, which states that the Constitution and the national government make up “the supreme law of the land.”

During the Republican administrations of Nixon and Reagan, many of the powers of the Federal government were transferred to the state and local governments. This policy was branded as New Federalism, but the actual process of the transference of powers is called devolution.

In the United States, state governments are set up with the same separation of powers—executive, legislative, and judicial branches—as the national government. The governor of a state is a member of the state executive branch.

The Supremacy Clause of the Constitution states that federal, or national, law is the supreme law of the land. This is a key component of American Federalism as opposed to the Confederation that existed under the Articles of Confederation. The Founding Fathers observed that under the Articles, the federal government had too little power and the states were free to make their own disparate laws absolute within their territories. Federalism and the Supremacy Clause remedies this situation by ensuring that all state laws must be within the realm of federal laws.

All fifty of the American states have their own constitutions; however, they are all also required to follow the national constitution first, which remains the “supreme law of the land” as established in the Supremacy Clause of the U.S. Constitution.

One of the core principles of the American political system is Federalism. In Federalism, power and legitimacy is shared by more than one political entity. In the United States, there is the national government, which retains the majority of control over the political arena, but there are also state and local governments, which have their own areas of power and an established legitimacy.