The nation state is a certain form of state that gets its legitimacy from serving as a sovereign entity for a nation as a sovereign territorial unit. The state is a political an geopolitical entity; the nation is a cultural and/or ethnic entity. The term "nation state" implies that they geographically coincide, and this distinguishes the nation state from the other types of state, which historically preceded it. If successfully implemented, this implies that the citizens share a common language, culture, and values — which was not the case in many historical states. A world of nation states also implements the claim to self-determination and autonomy for every nation, a central theme of the ideology of nationalism. (For ambiguities in the usage of terms such as nation, international, state, and country, see Nation).