Each delegates power to a national government for specific purposes. The United States under the Articles of Confederation functioned in a confederal system as did the southern states which seceded from the union in 1861. In a unitary government all authority rests with a central government. State and local governments have only those powers given to them by the central government. State governments in the U.S. function in a unitary system.
Federalism is the distribution of power between a federal government and the states within a union.
After the delegates to the Philadelphia Convention finished writing the U.S. Constitution, each state elected delegates to a ratification convention. Ratification was required by nine of the 13 states in order for the constitution to take effect. People were divided over issues of the extent of power of the Constitution, the degree to which the rights of states were protected, and the degree to which the rights of citizens were protected. Those favoring the new form of government, which divided power between a strong central government and the states, were called Federalists. Those seeking greater power for states were called Anti-Federalists.