A nation state is a political unit where the state and nation are congruent. It is a more precise concept than "country", since a country does not need to have a predominant ethnic group.

What is an example of a nation-state?

When a nation of people have a State or country of their own, it is called a nation-state. Places like France, Egypt, Germany, and Japan are excellent examples of nation-states. ... Even with its multicultural society, the United States is also referred to as a nation-state because of the shared American "culture."

What defines a nation-state?

nation-state, a territorially bounded sovereign polity—i.e., a state—that is ruled in the name of a community of citizens who identify themselves as a nation. ... Members of the core national group see the state as belonging to them and consider the approximate territory of the state to be their homeland.