Individuals develop allegiances to social groups, such as family, school, club, and religion, through processes of socialization; recent scholars have examined the connection of these more intimate processes to the maintenance or shift of political allegiances. Political scientists distinguish between natural allegiance, which arises from membership by birth within a political society; express allegiance, which arises from an oath or promise to support a political society, usually resulting from naturalization; local allegiance, in which an alien pledges temporary allegiance to a government for the protection it offers; and legal allegiance, which arises in certain cases from an oath taken to support a government temporarily, as when a foreign soldier joins its armed forces.

Under European laws a people did not have the right to change allegiance without consent of their governments. In 1868 the United States declared that it was the right of any citizen to voluntarily transfer allegiance to another government. Great Britain provided the same opportunity for its subjects in 1870, and thereafter other European states followed similar policies. The process of expatriation, however, is by no means universal.

See also Pledge of Allegiance.