A country made up of semi-autonomous units is a federation. In a federation, power is shared between the central government and the semi-autonomous units (such as states or provinces). The semi-autonomous units have some level of authority and independence in making decisions on matters that affect them, while the central government has the power to make decisions on matters that affect the country as a whole. The distribution of power and authority in a federation is usually defined in a written constitution, and there is a system of checks and balances to ensure that no level of government abuses its power.