The term nation state or nation-state, while often used interchangeably with the term state, refers more properly to a state in which a single nation is dominant. Over the last few centuries (and particular over the last half-century, except in Africa), this form of state has become more common, so that now most states claim to be nation states. However, this has not always been so; and even today there are some states where it is questionable whether they contain a single dominant nation. This is made more difficult by the question of what is a nation. There are many states, such as Belgium and Switzerland, with multiple linguistic, religious or ethnic groups within them, without any one being clearly dominant. However, often (and especially in the case of Switzerland and the United States of America) a national identity has been constructed despite these differences. A better example of a non-nation state would be the United Kingdom, which consists of the four nations England, Scotland, Northern Ireland and Wales. Although England was overwhelmingly dominant within the United Kingdom in the past, that can no longer be so clearly stated as the case.
A somewhat similar example might be contemporary Spain, where Basques, Catalans, and Galicians claim to be nations distinct from the historically dominant Castile (the Spanish Constitution of 1978 hints at this by mentioning "regions and nationalities" within Spain, and recognizing implicitly their pre-existence).
Historically France was more successful at subsuming within a Gallic nation-state such culturally disparate elements as Brittany, Aquitaine, Languedoc and Burgundy, though less so in Corsica.
In many cases, such as Canada, Switzerland, United States of America, Indonesia, the Soviet Union, India, and China, efforts will be made to create a national identity that encompasses different groups within that nation-state. In the case of China this effort has manifested itself in the concept of Zhonghua minzu (or a Chinese people).
Examples of non-nation states are empires which embrace more than one nation, city-states which may be part of a larger nation, thalassocracies, American Indian nations or tribes none of which possess states, and sovereign corporations (as in the Hudson's Bay Company or the British East India Company). The Palestinians are sometimes referred to as a Nation without a state, much as European Jews before the official creation of Israel in 1948.
One common situation occurs with a political boundary does not coincide with an ethnic or linguistic one. This often happens because political boundaries are distinct whereas ethnic or linguistic boundaries are gradual. In many cases such as the Rio Grande valley of Texas or the Chinese-Korean boundary along the Yalu River, ethnic identities can be reconciled with political ones. In other cases, such as with the Balkans this has not occurred and can lead to irrentenism and calls for ethnic cleansing.
Another common situation can occur when there are large numbers of people with a national identity outside the nation-state often as a result of a diaspora. One common solution is to create a political identity that is distinct from the ethnic identity. This has happened with Germans (reichdeutsch versus volkdeutsch) and Chinese (zhongguo ren vs. hua ren). In some cases the political identity includes people who do not have the ethnic identity as is the case with Kazhanstan where there is a distinction between Kazhanstani (which includes ethnic Russian citizens of Kazhanstan) and Kazhak.