The nation state is a state that self-identifies as deriving its political legitimacy from serving as a sovereign entity for a nation as a sovereign territorial unit. The state is a political and geopolitical entity; the nation is a cultural and/or ethnic entity. The term "nation state" implies that the two geographically coincide. Nation state formation took place at different times in different parts of the world, but has become the dominant form of state organization.
The concept and actuality of the nation state can be compared and contrasted with that of the multinational state, city state, empire, confederation, and other state forms with which it may overlap. The key distinction from the other forms is the identification of a people with a polity.