This origin is in the era when the ancient feudal system was established. The definition of a big country is composed of many smaller local governments (vassal States), which have no complete sovereignty, but are obliged to obey their big monarchs. The status and role of the vassal state overlap with that of the "vassal state", but the vassal state is a real country. For example, even the empire of the suzerain country can't exercise decrees in it, and residents often have cultural differences with the suzerain country, but they are in a state of forced alliance.

Because the princes of these small countries hinder social development, such as setting up checkpoints to collect taxes, and have some real powers in the territory that even the monarch does not have. Therefore, under the protest of leaders and the suppression of monarchs, in modern times, all the small vassal States were merged into nation-states or larger empires, while the vassal States gained independent status. Further, after the constitutional monarchy, the vassal States were annotated as separatist forces of medium or even big countries, or even the products of imperialism used to divide colonial people, while pretending to retain the privileges of the old royal family (such as India's native countries), rather than being truly abolished countries.

But on the other hand, it is also because there are still small ethnic groups who are not fluent in the main language objectively, and in order to reduce conflicts between them, major countries conditionally recognize the independent status of some vassal countries that were originally upgraded to sovereign countries, and the conditions are mostly permanent neutrality.