A nation is a group of people sharing language, culture and/or ethnicity. While today many nations can be identified with an independent state (a nation state), this was not always so; the rise of nationalism in the 18th and 19th century was when this idea (that each nation deserved its own state) became influential. There are still today however many nations without states, such as the Kurds or native American nations (see First Nations).
In common usage, terms such as nation, country, land and state are often taken as synonyms, i.e., for a territory under a single independent government, or the inhabitants of such a territory, or the government itself; in other words, a de jure or de facto state.
The idea of a nation is somewhat vague, in that there is generally no strict definition for exactly who is considered to be a member of any particular nation. Many modern states show a great diversity of cultural behaviours and ethnic backgrounds. England may be a classic example: a territory which is not a state, since it has no government of its own, and which has large immigrant populations and diverse cultural behaviour, yet which is often described as a nation.
Governments of stable nation states usually solve this problem by granting nationality to those born within the territory or who have one or both parents already possessing nationality. When granting nationality to immigrants, language and cultural knowledge tests are sometimes applied, but ethnicity is now often ignored to avoid racism and/or the accusation thereof.
Groups which are in some way culturally coherent (or are being claimed to be) are sometimes described as nations, despite not sharing a territory (see diaspora). Some examples of such concepts are the Romany nation, the Jewish nation, (especially before the creation of the state of Israel) the Melungeon nation and the Queer nation.