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. While people do talk of a 'British nation', it is questionable whether such an entity really exists. And 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).
The PRC still attempts to make herself a nation state. She set up Zhonghua minzu, the pseudo-ethnic group at the top of each ethnic group within "China".
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.