The nation-state rose along with other forces of Modernity as the preeminent form of polity. States usually have a centralized form of government whose power extends over its territory.
Government decrees passed by a state apply to all within its boundaries. These decrees are enforced in its territory by a civil authority - a system of administrators and beurocrats. The states power lies with its monopoly over the use of force - by controlling the army and the police.