Humans have always partitioned space to separate themselves from other human groups. This is similar to other species. The creation of territory is the basis for political organization and action. The political partitioning of space leads to the most basic of human geographic divisions - the sovereign state. Most states are recognized as such by other states, and their territory respected; they are governed by a recognizable body, with rules for the administration of the state. Individuals are therefore tied to a state and subject to its rules.
A nation is a cultural group which is based on variables such as language, religion, ethnicity. These factors give people a sense of identity and community. A state is a formally defined political territory, with a clearly defined set of institutions, including rule making and enforcement, that claims exclusive jurisdiction over all the people and activities within the state. A nation state is a clearly defined cultural group (a nation) occupying a defined territory (a state).
Historically, just because a political unit exists does not necessarily mean that the boundaries delimit a nation, or national identity, e.g., the Roman Empire and various other monarchies So how did the idea of the nation state arise? Required the concept of nationalism, which is the belief that the nation and the state should be the same or congruent, and that there is no other appropriate way to delimit a nation state. It is therefore the natural political unit.
It has also been argued that nationalism also means: that all members of the national (cultural) group have the right to live within the borders of the state; that it may be inappropriate for other national groups to live within the borders; and, the government must be in the hands of the dominant national group. Given these ideas or arguments, it is possible to see how conflict both internally and externally can arise. In Europe, nationalism became the dominant criteria for defining a nation in the 19th century. Before that most people just tended to accept whatever empire or despotic ruler was in charge. Why did this change?
Five possible explanations for the emergence of the nation state: • response to national political philosophies of the 18th century, especially the Swiss philosopher, Jean Jacques Rousseau (1712-1778) • desire to be closer to people of similar cultural backgrounds • part of the transition from feudalism to capitalism, because those who owned and benefited from the means of production liked a stable state (this is a Marxist argument) • the collapse of local communities (with industrialization) and the need for communication/technology and coordination of a larger group