Final answer:
Federal structures divide sovereignty between a national government and regional units, with bases for division including multi-ethnic or multi-national compositions and a balance of central and local autonomy.
Step-by-step explanation:
The division of a country into a federal structure often occurs for reasons including governance of a multi-ethnic or multi-national society, or the desire to balance a central authority with local autonomy. Federalism is a system of government where sovereignty is constitutionally divided between a national government and regional political units like states.
In the United States, federalism has evolved over time, with the constitutional logic of federalism delineating the division of powers. For example, the U.S. Constitution allocates certain powers exclusively to the federal government and others to the state governments, while some powers are shared.