Which characteristic is essential for defining a federal state?

A federal state is defined by a system of governance that allows for the division of powers between a central authority and smaller political units, usually called states or provinces. This system is essential because it ensures that while there is a central government that handles national or federal issues, the smaller units also retain certain powers and responsibilities. This division allows for regional interests to be represented and catered to in governance.

In a federal system, the smaller units might have their own laws, regulations, and governance structures, which enables them to address local issues more effectively than a centralized authority could. This characteristic promotes a balance of power, preventing the central government from becoming too overpowering and allowing for diverse policies that can better meet the specific needs of different regions.

The other characteristics given in the choices do not align with the definition of a federal state. A complete central authority would indicate a unitary state, whereas an absence of governing structures at local levels contradicts the very essence of federalism. Lastly, complete autonomy from international laws does not define a federal state, as federal states often still operate within the framework of international law while managing their internal governance.