Citizenship of the United States
A person who is considered a citizen by more than one nation has "dual citizenship". It is possible for a United States citizen to have dual citizenship; this can be achieved in various ways, such as by birth in the United States to a parent who is a citizen of a foreign country (or in certain circumstances the foreign nationality may be transmitted even by a grandparent) by birth in another country to a parent(s) who is/are a United States citizen/s, or by having parents who are citizens of different countries. Anyone who becomes a naturalized U.S. citizen is required to renounce any prior "allegiance" to other countries during the naturalization ceremony; however, this renunciation of allegiance renunciation of citizenship to those countries.
Afroyim v. Rusk
The concept of dual citizenship, which previously had been strongly opposed by the U.S. government, has become more accepted in the years since "Afroyim". In 1980, the administration of President Jimmy Carter concluded that the Bancroft Treaties—a series of bilateral agreements, formulated between 1868 and 1937, which provided for automatic loss of citizenship upon foreign naturalization of a U.S. citizen—were no longer enforceable, due in part to "Afroyim", and gave notice terminating these treaties. In 1990, the State Department adopted new guidelines for evaluating potential loss-of-citizenship cases, under which the government now assumes in almost all situations that Americans do not in fact intend to give up their citizenship unless they explicitly indicate to U.S. officials that this is their intention. As explained by Peter J. Spiro, "In the long run, "Afroyim"'s vision of an absolute right to retain citizenship has been largely, if quietly, vindicated. As a matter of practice, it is now virtually impossible to lose American citizenship without formally and expressly renouncing it."