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.
Lawful permanent residents (United States)
Green-card holders married to non-U.S. citizens are able to legally bring their spouses and minor children to join them in the USA, but must wait for their priority date to become current. The foreign spouse of a green-card holder must wait for approval of an "immigrant visa" from the State Department before entering the United States. Due to numerical limitation on the number of these visas, the wait time for approval may be months or years. In the interim, the spouse cannot be legally present in the United States, unless he or she secures a visa by some other means. Green-card holders may opt to wait to become U.S. citizens, and only then sponsor their spouses and children, as the process is much faster for U.S. citizens. However, many green-card holders can choose to apply for the spouse or children and update their application after becoming a U.S. citizen.