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.
Tax advantage
However, there are international limitations regarding tax advantages realized through pensions plans. If a person with dual citizen in the United States and in the United Kingdom, they may have tax liabilities to both. If this person is living in the United Kingdom, their pension could have tax advantages in the UK, for example, but not in the US. Even though a UK pension may be exempt from UK tax, it doesn’t necessarily mean that it is exempt from US taxes. In short, a US Tax payer with dual citizenship may have to pay taxes on the gains from the UK pension to the United States government, but not the United Kingdom.