The nation state is a state

State (polity)

A state is an organized political community, living under a government. States may be sovereign and may enjoy a monopoly on the legal initiation of force and are not dependent on, or subject to any other power or state. Many states are federated states which participate in a federal union...

 that self-identifies as deriving its political legitimacy from serving as a sovereign

Sovereignty

Sovereignty is the quality of having supreme, independent authority over a geographic area, such as a territory. It can be found in a power to rule and make law that rests on a political fact for which no purely legal explanation can be provided...

 entity for a nation

Nation

A nation may refer to a community of people who share a common language, culture, ethnicity, descent, and/or history. In this definition, a nation has no physical borders. However, it can also refer to people who share a common territory and government irrespective of their ethnic make-up...

 as a sovereign territorial unit

Sovereign state

A sovereign state, or simply, state, is a state with a defined territory on which it exercises internal and external sovereignty, a permanent population, a government, and the capacity to enter into relations with other sovereign states. It is also normally understood to be a state which is neither...

. The state is a political

Politics

Politics is a process by which groups of people make collective decisions. The term is generally applied to the art or science of running governmental or state affairs, including behavior within civil governments, but also applies to institutions, fields, and special interest groups such as the...

 and geopolitical

Geopolitics

Geopolitics, from Greek Γη and Πολιτική in broad terms, is a theory that describes the relation between politics and territory whether on local or international scale....

 entity; the nation is a cultural

Culture

Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...

 and/or ethnic

Ethnic group

An ethnic group is a group of people whose members identify with each other, through a common heritage, often consisting of a common language, a common culture and/or an ideology that stresses common ancestry or endogamy...

 entity. The term "nation state" implies that the two geographically coincide, which distinguishes the nation state from the other types of state, which historically preceded it.

The concept of a nation state is sometimes contrasted with city state.
The origins and early history of nation states are disputed.