The concept of federalism as a type of regime was literally invented in the eighteenth century, and it is a worthy addition to Aristotle's taxonomy of "cracies." Federalism is a constitutional principle providing for two layers of government: a central government, and a lower level of government - provinces, regions, republics, or states - with some kind of chamber to represent the lower units in the central government, and usually some provision for guaranteeing the integrity of the lower levels of government.