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.
International Traffic in Arms Regulations
This means that a person who was born in the UK but is a U.S. permanent resident working in the U.S. for a U.S. company will be considered a U.S. person only (under the definition of "US person"). If, however, the same person emigrated to Canada, obtained Canadian citizenship and commenced employment with a Canadian company, she would be treated as a Canadian-UK Dual National for the purposes of any U.S. export authorization to which her employer was a party. If she did not obtain Canadian citizenship but instead became a temporary or permanent Canadian resident, she would be treated as a UK Third Country National for the purposes of such U.S. export authorization.