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.
Birthright citizenship in the United States
Another problem arises where a Canadian child, born to Canadian parents in a U.S. border hospital, is treated as a dual citizen and added to the United States tax base on this basis despite having never lived, worked nor studied in that nation. While Canadian income tax is only payable by those who reside or earn income in Canada, the U.S. Internal Revenue Service taxes its citizens worldwide. Campobello Island is particularly problematic as, while legally part of New Brunswick, the only year-round fixed link off the island leads not to Canada but to Lubec, Maine—leading to many Canadians whose families have lived on Campobello for generations not being able to claim to be born in Canada.